As a child I suffered an accident in which a chunk of flesh was torn from my forearm. This resulted in a nasty scar. Later, as an adult, I noticed several hairs growing from this scar tissue. These hairs are similar in size and color to the rest of my arm hair. This makes me wonder if hair follicles can develop spontaneously.
I would think the existing hair follicles on your arm are somehow now re-growing out of the scar, because hair follicles do not develop spontaneously.