Grayshirts/deferring eligibility don’t cost any years towards your eligibility. It’s actually how a lot of Ivies get around the self imposed no redshirt rule and the academic requirements. This year also didn’t count towards anyone’s eligibility so he’s coming back as a true freshman with 5 to play 4 like you said. With that said, it wouldn’t be a surprise to me if you see a lot of the younger classes turn down that year in the future honestly unless they’re top tier guys.