Crossing the white line and into oncoming traffic is what they pulled him for, the pass was perhaps unwelcome (but not surprising, nor that close) but the cyclist stopping and chipping in with 'have you seen this' and wide angle video will make for a third subject of conversation. Presumably that driver will now observe better to the front, rather than just think "bike must pass" but I'm sure that their rear observations will be much more thorough (or actually done!) hell an equally brain dead moton could have been overtaking!