I sorta expected as much. Everyone says if bees have too much space to defend, SHBs thrive. Okay, I'll go along with that, but the converse seems also to be true, judging by your experience and mine. That owl box was full of comb and had lots of comb built and filled outside, as well. Lots of bees. I made the mistake of trying to transfer comb into frames with rubber bands, and that just gave the SHBs a new home.
I would suggest that when we encounter a box like that we should shake the bees into a "new" hive body with drawn comb, burn the old box, honey and all, and give the bees a couple of frames of comb with brood and eggs. Feed as needed. Some SHBs will get in the hive with the bees, but the vast majority will die, and if the new box is appropriately sized, the bees will be able to take care of the situation.
I hate to lost the Brood and honey, but that's better than losing the bees.
I hate to lose the honey, but