Meh. Miles did the same thing last year. It means nothing and I often feel only slows a player down more than anything else. Adding 2-3 pounds, yet much more strength, in one offseason while maintaining one's quickness and explosiveness is in my opinion a better way to go. But maybe his body was still filling out.
Hayward was what, 210-215 his rookie year? That isn't cutting it for someone who is 6'8. He should be around 225-230 now which is where he should be. He will lose some of that muscle during the season most likely, so he will probably be playing in the 225 region for most of the season.
225 is heavy for an SG. It's not impossible, but most quick SGs are 200 - 210 lbs.
He was maybe 200 lbs soaking wet last year. 215 seems very ideal for SG, wouldn't gain anymore or will be Harpring like.