I sat and watched him a bit while drinking my coffee and he likes to stand on top of this rock thingie in the tank.
He must have stretched WAAAY out and somehow reached the edge of the lid; then hoisted himself up and out through the opening in the back (where the filter used to be when I had fish).
One of my Betta fish died sometime last week, so now my other one is really lonely. The tank needs cleaned. Still debating whether I should just take out the divider and give this guy the whole tank for as long as he lives, (and then shut it down - I'm tired of fish) or whether I should go save another one of the poor Bettas in the plastic cups at the pet store.