Cal.... let me share.

He needs to keep a close eye on it. I had the exact same thing years ago!!! and it was removed. 10 years later after two biopsies they found a tumor IN my tongue... and yes IT HURT.

I am not saying it's cancer I am not saying it will become cancer, I am saying he needs to keep a close eye on it and see someone every six months particularly if it persists. It cannot be ignored. Plus if it becomes more painful and worse he needs to go back right away.

My first biopsy came back the same as his.
My second one came back inflamed tissue (they had removed the plack years before it had healed in that area, but a tumor grew UNDERNEATH so there was no sore or lesion just redness and pain)
a few years later it had developed into an actual lesion and it was a stage 2 cancer.

He needs to be diligent. He's young. It's very rare, but not unheard of.

I am a veg head, have never smoked or drank in my life.
I believe it was related to chronic irritation by a tooth in that area.

best of luck. and yay on the cancer free.