Thank you for your query,
The bump id due to formation of hematoma
in the scalp
layers above the skull bones.
Watch for abnormal symptoms like vomitings, abnormal behaviour, drowsiness
, bulging of anterior fontanellae, paucity of limb movements and if you find any abnormaility report to emergency.
At present as he is fine and playful, nothing to worry.
But consult your Pediatrician
for the examination to look for any abnormal signs.
Hope I have answered your query.