Little holes happen a lot.
They happen less with pristine water.
They bump and scrape their tails on things... although it it quite possible that it is finrot. Watch out for the holes... if they are steadily getting bigger, I would remove him and treat him with salt...
If it gets worse, you may have to medicate
If you could post a pic, it would be easier to diagnose
For now, keep the water clean, treat with some salt, and feed nutirent rich foods