If you read through the posts, the OP came back and stated that he DID do a walk-around before leaving the campground. He said that he sensed there was something "off" but couldn't identify it. He double checked all his "before driving away" checklist items, but the missing tire/holder didn't register.
He also said that the TT bedroom is in the front and that they had the A/C going all night.
So, it still doesn't prove stolen over lost, but makes stolen less "unbelievable".
For me, in situations like this where it really could have been either way (stolen or lost), I choose to believe the one that is less negative towards other folks. It feels better to me.