Not sure where you're getting this from. The video starts with the young man coming onto the older couple's (leased) property, picking up their plant pots and dumping them at their front door, then waving at their camera and yelling to gain their attention. All the footage comes from the same viewing angle, so it's clear that the entire video is from a CCTV camera at or above the older couple's front door and everything we see takes place in front of their house.
This is also made clear by the narrative of the events in the interview they gave to The Sun newspaper. And although the older guy did aim a slight kick at the younger guy, even if he made slight contact (which it's not clear that he did) that is absolutely no justification whatsoever for prolonged frenzy of violence he was then subjected to.
The older guy was punched twenty-two times in the head, after he was already lying unconscious on the ground. And these were not light taps, these were full swings of each arm, against a motionless, unconscious and therefore defenceless older opponent. In what universe is that justified by an attempted kick out that as far as I can tell, might not even have landed?