You have not mentioned the age of your child.Eye lid swelling post blowing is not a very common phenomenon.Hence the CTScan must have been done to rule out extension of the bleed or fracture
The reason for spontaneous eyelid swelling the most common reason is an injury
around the eye post trauma,an infection ,fragile blood vessel and blood disorders and also a spontaneous shoot up of blood pressure .
Since it is an eye problem he should be referred to Ophtalmologist who could assess and check the pressure of the eye.
At present you could keep the eye clean with water and could give him painkiller if it pains.