All newborn colts distend theirs, but usually after birth, if it was distended during birth it may have gotten injured during delivery. I would call the vet asap, and note if any urine dribbles from the navel as well. If the penis is swollen it is a red flag and means a call to the vet. Maybe the owner could apply some cool wash rags to the area until the vet arrives to help stop it from swelling any more.