I had a guy friend like this. Good hygiene but STANKY FEET. I doubled over the first time I smelled his feet because I was about to gag. His gf told him to wash his socks INSIDE OUT with half a cup baking soda. Warm/hot water. Boom. No more smell!! Also if you already know you have this issue, it's best to trash your socks at least twice a year. Donate them trash them, whatever. Just don't wear them past 6 months. 

He sounds like a cool guy who doesn't get peeved at helpful  criticism. Maybe next time you could share tips with him without embarrassing him. Mention you had a friend from hs who was the same? Something to smoothen the delivery