My 9 Year Old Son Headbutted With Another Student 4

My 9 year old son headbutted with another student 4 days ago. My son has been his normal self all this time. No vomiting no confusion no headaches. His eyebrow rim was the area of contact causing his eye to swell first 2 days now it's purple green and blue. He expressed to me today he had a small headache. He had a bloody nose last night
I thought he might be dehydrated due to the hot weather. Gave him lots of water headache went away. Do these headaches happen after?