I do wonder what Bela thinks about all day. He likes to snuggle, or scrunch himself, up against the heater. My other betta, departed maroon Fred, liked to bury his head under the rocks in his bowl. They were mostly lightweight plastic nuggets and he would shift them around with his snout (or whatever the very front of a fish is properly called) and wedge himself under and among them with the rest of him pointing up. I think bettas find it comforting to be pressed into tiny spaces. Bela might bury his head too if he didn't have his jar complex to hide in.
I like trying to figure out the extent to which he has a personality. He must have at least a bit of one, or else every member of his species would act the same way, and I'm pretty sure most of them don't do a threat display at square objects. Fred never did. He did his threat display at Kiyo the rat, which was entirely reasonable, as Kiyo actually wanted to snatch and eat him.