Ben,
I know exactly the type of session you are describing and if I were there I would do exactly the same as you.

However the sort of session I usually attend is packed out with musicians at all levels and most of them have a wide repertoire of English/Irish/Scottish. Most of the night once a set starts up everybody pitches in and any beginners can easily fit in quietly without spoiling the overall sound. Most of us are ear musicians and this is the quickest way for newcomers and beginners to pick up the repertoire. It's how I picked up most of my tunes.