It's that. Goosebumps are caused by the tiny muscles at the base of your hair follicles contracting, causing our hair to stand on end and covering our skin with tiny bumps.
There is really no reason to have this reaction anymore as it's of no use to us. But it was useful to our ancestors who were a lot hairier.
Goosebumps raise the hairs on an animals for two main reasons. First, if the animal is scared, its hair stands on end to appear bigger which might be enough to make a predator change their mind about going after it.
Above: not bear-food.