Why does your roof get blisters? Typically it’s because of heat buildup. The shingle gets hot, the asphalt bubbles up, and then when it cools, the bubble goes away. However, the blister has loosened all the granules in that little bubble, which causes the granules to fall out. The primary cause of blistering is lack of adequate ventilation in the roof. Note also that not having adequate ventilation could void your shingle manufacturer’s warranty.
If you get a home inspector, or even a roofer, who says that you have hail damage, request to see the photos they’ve taken of the damage. If you see that it looks more like a blister than hail damage, then it would be wise to get a second opinion.
Bottom line, if you’ve had a home inspector tell you that you have hail damage, don’t file an insurance claim right away. Rather, be sure to ask a reputable roofing contractor to check that the inspector isn’t mistaking shingle blisters for hail damage.