Will be sending prayers for him!
Years ago when we lived in Georgia, we had a sorrell Gelding that had the same type of lump, vet checked it said it was nothing, it went away, and came back. This happened a few times over the year, we could not for the life of us figure it out since the vet said it looked as if he had been kicked.
He wasn't with the mares, and the stallion and he were not turned out together either.........found out after keeping vigils for weeks, it was my husbands Saneen goat head butting him! They had done a lousy job of polling him and the horn stubs were causing returning hematomas . Although they were best friends, needless to say they were no longer allowed to play unsupervised!

Hope it is just as harmless for Austin! Good thoughts heading your way!