welcome to healthcare magic ....
The bump would be 1)just fluid accumulation due to direct injury
as a result of inflammation. 2) could be a collection of blood .
If he had vomitting or loss of conciousness after the fall , then he should get a CT scan
done to look if there is any injury to his brain.
If no vomitting or loss of conciousness after the injury then - no need to worry the bumps would take a week or two to disappear.If you are really concerned and want to get it reduced faster can use serratiopeptidase
tabs which reduces inflammatory swelling.