That does look a lot better!! Clean, warm water can work miracles!!
I'd mostly seen the nastiest looking rot on his anal (bottom) fin, and I'm still seeing a little nastyness, but it's a lot less dead looking. He's on the mend!!
Sounds like he's a very happy fishy!! He might actually slow down some one his fins come back, shorter tailed bettas tend to be a little zippier. And as his tail grows in, the flow of the filter may start bothering him, as his whole backside will be a giant sail.
It's very normal to try to get to the 'food monster', my fish will come beg at the edge of the glass, and follow my finger around the top, or if my hands are in there, they nibble at them. So cute.
The moss video is super cute!! Just keep an eye out if he's rubbing of 'flashing' against anything else, it can be a sign of parasites, they're itchy and make fish scratch on things. Looks like he's just playing here though :3
Cannot WAIT to see how he grows back!! He's very lucky to have you!