It was noticed before he had any interaction with vaccinations, so we know it had nothing to do with that.
Yea. Ok
You realize, of course, that if your child was born in a hospital he was likely given the HepB vax at 1d of age with or without your express permission.
And probably got a booster at either 1m or 2m of age along with his other 2m vaccinations like DTaP, polio and HiB.