Haha so cute! Definitely a 'i'm not doing anything wrong mummy' face!
I remember getting the same face when my boy discovered I had stored some treats in his big plastic storage box. I was keeping it outside his stable for this reason, I removed the treats, tied him up outside his stable thinking 'treats are gone he won't bother with the box'. Came back two minutes later and he was stood shock still with his front leg IN the box. He didn't move a muscle and just watched me come back into the stable block like 'who me? I'm just stood here minding my own business' like he did it everyday. Silly boy!