Q:

Passport requirements on entering Ireland as a citizen

Basic premise of this question is what are usual requirements for entering Ireland through Airport Immigration - and does this change based on where you departed from?
Basically - I'm a citizen and resident of Ireland - I was travelling back to Ireland last week from the United States and as I was going through Immigration check in Dublin Airport I presented my Passport Card.
This card, in general - I've used multiple times for travel between Ireland and the EU without any sort of problems - and it's far easier for me to access in my wallet than to dig out my physical passport book out of my backpack.
However, when I was going through Immigration in Dublin Airport on arrival from the US, I presented the passport card and was then asked where I was coming from.
When I replied that I had departed from the United States the immigration officer requested my actual physical passport.
I didn't really mind - nor did I want to argue the point - so I produced my passport from my backpack.
However it got me thinking and my question I guess - 

For what reason would Irish Immigration need to see my Passport to enter the country of my citizenship - provable via the Passport Card.
What would have happened if I refused or lost my actual passport?
As a citizen of the country, am I obliged to tell the immigration official where I was arriving from?

A:

As an Irish citizen, you have the absolute right to enter Ireland. The immigration officer cannot possibly deny you entry, as long as you produce a document that shows you're in fact an Irish citizen - and the passport card clearly shows that. Therefore you have the absolute right to only produce your passport card and refuse to provide any other document. It might delay your border crossing though, so personally I'd just show my passport if I actually had one with me. 

A:

The Passport Card is valid only for travel WITHIN the EU/EEA/CH.
I've had this same issue. Was returning to Dublin on a flight from Moscow. Was asked where I was coming from (which was fairly obvious as there was only one flight coming in at that time).
I'm a Canadian dual-citizen, so it would be handy to travel to there or the US on my Canadian passport and return to Ireland with the card that lives in my wallet. Pain in the backside, and I don't really understand the point of it, but that's the way she goes.
EDIT: Here is the link to the DFA page stating the same: https://www.dfa.ie/passportcard/

A:

It is first important to note that there are no absolute rights to anything in Ireland. All rights can be limited by Acts of the Oireachtas, or by relevant Statutory Instruments. 
Irish citizens are entitled to enter Ireland, regardless of the document they use.
However, you are required to use the passport card number when checking in online if you intend to use it (at which point the airline can refuse to carry you if your flight originates outside of the EU).
If anything, this makes sense for logistical reasons:

Airlines have to register their passenger manifest with the country they are travelling to (including the document numbers of the passengers on the flight)
From a security standpoint, if a person arrives at immigration,without a travel document that matches a document from a registered passenger manifest, a security failure/breach may have occurred (either in an Irish Airport, or the originating airport). 

This would need to be rectified. The only way to understand if this has occurred is to ask for the document you actually traveled on (in this case your passport book)

Additionally, your passport isn't actually your property, it's the property of the Minister for Foreign Affairs. As such they can request to see it, if only to ensure that you haven't misplaced it on your travels.
There is no requirement that entry to Ireland be given without any delay upon proof of Irish citizenship. They can't refuse your entry (as an Irish Citizen), but they can certainly delay it if they have a reasonable justification. For example:

you may need to be quarantined if you arrived from a country with an active pandemic outbreak to ensure public safety
you may be the subject of an arrest warrant
you may be the subject of extradition proceedings
ensuring there hasn't been a security breach in the air travel system

What would have happened if I refused or lost my actual passport?

If you lost your actual passport you can tell them that, and you will likely need to make a statement to the Gardai about the lost passport while you are still in the airport (lost passports are at risk of being forged and used to facilitate illegal entry into the country).
If you refused then they are able to escalate it to the Gardai, and a Garda can demand to see your passport (failing to comply with Garda orders is an arrest-able offence under the Criminal justice (Public Order) Act).

Are they allowed ask where I have traveled from?

Of course. There are different customs requirements and regulations depending on your point of origin.

