Only tickets sold by Aer Lingus count. Regardless of where sold in the world it will be issued as a 053 if sold by Aer Lingus. Every ticket with a EI segment should have a EI PNR with 2 at the start regardless of who sold it.
It looks like whoever sold you the ticket plated it on a different airline, this is rare and likely to be a travel agency involved or as part of a ticket with other flights.
First 3 digits from the ticket?
3 digit or 4 digit flight number? greater than 4000?
Fare class, ?