That was Kockett, he was acting the gowl as he always does. He had a great game in fairness to him. The ref didn’t actually penalise him, it was one of the forwards after him.For the last ruck before the try, one of the Castres players was sitting up complaining at the ref, no attempt to rejoin the line.
Maybe his leg was stuck in the ruck but in that situation you have to make some effort. Might have given them an extra man to stop the try.