Looks a bit like what we had on one of our fatteners, the butcher told us if it wasn't bothering the pig to leave it alone and it would disipate itself. They can be caused by knocks. (happened to be on the phone to him hen i noticed it) Vet said the same and he was right it disappeared within a few days.
Would suggest you monitor.
Bursting it will only make it gammy and prone to infection.
If it becomes a problem or pig goes down hill, ring vet as will probably need Antib's.
hth
mandy