It is difficult to say without seeing what is happening myself, but …
From my observations here a dominant male would not tolerate another male being so close, even if he wasn’t particularly interested in the female. So my guess would be (if the drinking hog was definitely male) that he was chancing his luck in the hope that the ‘courting’ (more dominant) hog was too busy with the female to notice him. It sounds as if he may have been right, but maybe the ‘courting’ male noticed him leaving and went after him, to potentially biff him, out of sight. The more dominant male is not always the biggest one. By then the ‘courting’ male may have been well distracted and so didn’t bother to go back to the female, who he may not have found interesting enough anyway – possibly a youngish female.
Of course, all of this is surmise, but an alternative interpretation. You may just have a very tolerant dominant male there! Also if the drinking hog was a female that would be a whole different scenario! Other females will often eat/drink close to a courting couple, but he may have just noticed her when she left and so went in pursuit.
I think you will learn to work them out better if you keep on watching (preferably in real time), but they will probably always have an element of mystery, not least because we can’t see enough of them (with them disappearing into the undergrowth, etc.). But, perhaps that is part of their charm.
You really need to see certain types of behaviour over and over again with different hogs to be able to reach any sort of conclusion about what they mean. Preferably knowing who the hogs are (from their natural markings) and definitely whether they are male or female. The small clips from videos are simply not enough to get a good ‘picture’ of what is going on and can too easily lead to wrong assumptions. Also with hogs there can always be a curved ball thrown in, so that it isn’t always possible to be certain about a particular piece of behaviour. If you are really interested in hog behaviour, it takes time and patience, but can be very rewarding. Once you have learned certain behaviours you can then look at, for instance, a video, and recognise those behaviours with a degree of certainty, if not always absolute certainty!