My 7 Year Old Son Hit His Head Hard On

My 7 year old son hit his head hard on a wood. I immediately put ice compress. The bump was reduced. He did not show any signs of fever, vomiting, or headache. He is perfectly fine, aside from a small bump on forehead. One day after the bump on his forehead swell and looks like he had a black eye on both eyes.what causes the black eye?is there something wrong? Thanks!