Betta gets fear stripes when eating??

hi everyone!
so a little background here. my bettas tank recently spiked in ammonia while i was away on a trip. I am really not sure how this happened. my pet sitter did the best they could to care for him while i was away. they did a water change and kept him as low stress as possible. he seems to be recovering he does have ammonia burns on and around his face. the underside of his face is also white, is this normal after ammonia poisoning? just wondering because i have never had this happen to other fish before. he’s swimming fine and acting more normalish now. this was about 2 weeks ago. however the last few nights when i have fed him he gets fear stripes. he still eats his food and they will go away shortly after he is done eating they are also not their before he eats. I have never had this happen with any other fish and i couldn’t find much online about it. should i try different food? and what do you recommend I do? also one more thing is a recently set up a quarantine tank for another sick fish of mine and it is next to his tank, there was not room anywhere else. there is a large price of cardboard between the tanks so they can’t see each other. i was wondering if it was maybe the new sound of the tank stressing him? I don’t know i’m just listing possibility’s of what it could be.

thank you in advance for and responses!
( also ecxuse my non capitalized letters my keyboard is broken)

The lines on his body could be aggression stripes and not fear stripes. But if he is eating well, I wouldn't worry about the stripes. The cardboard between the 2 tanks might be causing him to see his reflection in the glass and getting grumpy at that.

White patches are not normally associated with ammonia burns. However, they are regularly seen on fish that are in poor water quality or exposed to chemicals/ poisons, or have an external protozoan infection. Bettas don't normally get external protozoan infections when kept on their own but can get them if the tank isn't cleaned regularly.

Do a 75% water change and gravel clean the substrate every day for a week and see if the white goes away. if it does, then it's caused by something in the water irritating the fish.

Pictures and a 1 minute video of the fish eating might help with identifying health issues.

this is a picture on him as you can see the under side of his face is white. you can somewhat see the burns. I will do a water change today when i get off school. also last night i tried giving him a different food , some pellets i had instead of flakes and he didn’t show any stripes so maybe it’s just the flakes he does not like? i’m going to go to the pet store later today to get more water test strips should i maybe get another food because the pellets i have are not the best quality.

I can't tell much from the picture, it's a little blurry

He does look slim and could need more food. You can try frozen brineshrimp, bloodworm and mysis shrimp. You can also buy frozen prawns from a fish shop or supermarket seafood section. Keep them frozen and when you want to feed some to him, take one out and defrost it. Remove the head, shell and gut (thin black tube in his body) and throw these bits in the bin. Use a pair of scissors to cut the remaining prawn tail into little bits and offer him 1 or 2 bits at a time. Let him eat until he's full. Then stop feeding and remove uneaten food. Put the remaining prawn in the fridge and use over the next couple of days before discarding the leftovers. If you keep most of the prawn frozen and cut a small piece off, then you won't waste as much.

sorry it took me so long to reply. but i will definitely look into getting frozen foods . the white underside of his face is gone after i did a water change. however he is still doing the stripe thing when i give him his flakes. i wasn’t able to get different food yet so he’s still on his original flake food. but i did get a picture of what his stripes look like. I know the first ones a bit blurry but it shows how dramatic they are after he first eats. the second one is about 2 min after he was done eating but the stripes were already disappearing. i have timed it and about 5 mins after he’s done eating the stripes are completely gone. he does not act any different when he is showing stripes either they just kind of appear once he starts eating.