If my boyfriend is working full time throughout the year and took care of himself,can his mom still claim him as a dependent even though he filled head of household ?

I have done his taxes for him the last two years online. She knew that he filled and still continued on claiming him. Her theory is " if he made less than $10,000 she can claim him" well he made over that . H & R block said the only way she can claim him is if he was in school or college but he wasn't.