I'm glad it's not just me! There was a tiny gap in the corner where the boards met. He emptied his pouches first to squeeze through
. I think he has quite an adventurous personality. He doesn't seem scared of anything, and he's had a lot of changes recently. I think he sounds like your Willow. An explorer!
Mind you, the first thing he did when back in his cage was to have a bath in his sand. Clearly the cobwebs didn't feel too good.