What you’re describing sounds like it was the customs check. Pre-brexit, if you were arriving from the EU, then there was no customs check since we were all part of the same customs union.
From a customs perspective, flying from one EU country to another EU is treated like a domestic flight.
If I (a British citizen) flew from London to New York, then on to Chicago; I'd expect to go through customs when I arrived at New York, but not when I arrived at Chicago.
What you’re describing sounds like it was the customs check. Pre-brexit, if you were arriving from the EU, then there was no customs check since we were all part of the same customs union.
The usual flow is
immigration check -> baggage collection -> customs check