tiger oscar lump?

Hello! This is Pumpkin, I rescued him from a pretty horrible living situation (I'll put his story down below for those who are curious), but he has a lump on his side. The surface of the water is moving so some images are blurry but I tried to get some good ones. I was wondering if anyone could tell me what this is or if they have encountered it themselves. It has gotten a tad bit bigger in the 1.5months we have had him. No noticeable behavioral changes however. I'm worried about my little guy, we've basically become best friends now and I would hate for him to not be feeling good.

Pumpkin is roughly 4 years old. Staple diet of Dainichi oscar pellets, occasional freeze dried krill as treats, 0 ammonia, 0 nitrites, 10 ish nitrates, 100gal tank, 2 common pleco as tankmates, frequent 20-25% water changes, fluval FX5 canister filter.

Pumpkin's old owner was a friend's late roommate who unfortunately passed away in December. They had nowhere for Pumpkin to go, and after meeting Pumpkin I immediately offered to rescue him after I got very concerning information regarding his care:

He was in a 60ish gallon tank with two giant pleco, the water was black/green with about a 2" thick layer of poop on the bottom of the tank. He had a shitty automatic feeder with goldfish flakes for years, they would feed him hotdogs and other garbage/whatever he would eat that they thought was funny. Parameters were the worst I'd ever seen in my fishkeeping years, he was so pale and colorless before we got him, basically every aspect of his care was negligent.