I feel he is pretty ok.
If he hasnt got immunized for tetanus, he need to get a Tetanus toxoid vaccination
Normally projectile vomiting
ie throwing off like vomiting, severe headache
, sluggish movement of pupil, seizures should be watched for after getting a blow in head.
Since he doesnt have above mentioned symptoms it seems he is ok.
The heamatoma( swelling due to blood collection) will subside on its own, dont massage it.
If anything out of normal happens take him to paediatrician he may request for a CT scan.