That is the (good and bad) thing about those white snakes..
You see everything !
I agree, might be a small rub from something sharp, or just some "dirt" got in between scales. Try cleaning it up with a wet cloths. If they are small scabs/wounds instead of dirt, keep an eye on it. Watch for more spots popping up or the ones that are there getting bigger.
In which case there might be something fungal going on, or some bacteria entered the small wounds.
Hopefully it will clear right up, though !!