Hello again and thanks for waiting.
I have worked out an answer for you below ...
1. Yes it is very possible that this was caused by a bite of some kind or perhaps some other sort of traumatic injury. Also you can sometimes see this sort of appearance where abscesses or cysts have burst to the surface.
2. It is very encouraging that he is his normal self at present but the swollen bump you are seeing may mean that the wound is infected. For that reason it would be best to have your vet check things over just in case as prescription drugs such as antibiotics may be needed.
3. In the meantime until you can get to a vet you could poultice the area with warm salt water twice a day. Use warm water from the tap and saturate it with table salt. Just use kitchen paper soaked in the salt solution and place it over the affected area, change it frequently so it holds the heat. Once you have done this gently dab the area dry with some clean kitchen paper and apply the likes of Neosporin into any open areas.
I hope I have covered your question fully enough but if you would like further clarification or to talk things over a bit more then I will be on-line for the next hour or so and I will be more than pleased to continue working with you.
Please be kind enough to rate my service to you after we have concluded our dialogue, such feedback helps me maintain the quality of my answers.