Sounds to me like the poor hog has been marked by an excessive marker.
Re. the belly rubbing – if that’s the reason, it isn’t working if the hogs here are anything to go by. I always think it is more of a sinking and lengthening of the whole body, rather than a chin rub. They seem to do it here when there is a female around. It seems to be part of the courtship ‘dance’. They also usually seem to ‘shorten’ (and widen) their faces at the same time. I always think it looks as if they are trying to impress the female. They sometimes do similar just after a female has left.