Head injuries notoriously bleed profusely, often look much worse than they are.
He's very likely to have sustained injury in crash landing, which of course doesn't also rule out being whacked on the head by someone, but if I was a betting person I'd be putting money on injury sustained while falling out of the sky at high speed.
A head injury is any trauma to your scalp, skull, or brain. Head injuries can range in severity from a mild bump on your head to a serious brain injury.
healthcare.utah.edu