Fuzzy bump on leg of unknown origin, help appreciated

Hello!
My boyfriends axolotl developed a small fuzzy bump on it's rear leg sometime in the past 24 hours. There is another small bump right behind the leg on the tail, but it is not fuzzy (you might barely be able to see it in the pictures). His gills are also curled forward quite a bit which is very unusual for him, so he appears to be under some sort of stress.

He did a water change yesterday, that is the only recent change to his tank. He's bringing me a water sample to test tomorrow so I don't know the water parameters at the moment but can update later. He did previously have an artificial plant in the tank that wasn't super sharp but could have scratched the axolotl, he did often hang out in the plant so that's possible. The plant was removed today after noticing the lump.

The axolotl hatched in October and is about 5 - 6 inches long. My boyfriend's very worried about him, so any advice would be greatly appreciated, I haven't seen this on any of my axolotls before.

Hopefully the attached pictures are helpful!

It may be some sort of fungal infection. If it is at an early stage then just keeping the axolotl in excellent water conditions could help it to clear up without further treatment. If not then I hope that the following information helps Axolotls - Health & Diseases
Are there any other symptoms? Has he gone off his food?
If his plant has been removed he may be a little stressed if he enjoyed hanging out in the plant, so it may be worth replacing it, perhaps with a silk plant (something soft).
I would keep a close eye on it for now and see how it develops.
However, I'm quite new to axolotls, so more experienced keepers may have better advice.
Best of luck for a full recovery for your little one.