If hecwas unsettled the stopping is fair enough, a different reaction when the pizza pricks pulled by P187 may have diffused the situation immediately, although I'm not so sure with their attitude. It's not an uncommon reaction by a rider that's had someone fly up to a junction like that, and if the pizza guys were going to head the other way they shouldn't have come after him, although their road position at the junction wasn't great for turning right.
As with any incident, in most cases both parties could have done more to avoid it, and in this case not to aggravate it. If another biker had come in hot to the junction, I would expect that they'd have pulled over and apologised. Thise who ride on L plates for a job are less likely to have the same mentality as those who choose to ride.
I do think that companies that allow platers to ride for them should offer more training than just the CBT. I know Pizza Hut in Leeds send their riders for extra training at one of the rider schools, and having seen them ride, they appear to be quite safe and sensible. Unless it's all gone a bit wrong, you really shouldn't approach a junction at that speed, get it wrong and there's nothing left in reserve.
So in short, if there's two avoid confrontation, same if there's one, but if you own a delivery company running 125s, make sure your riders can ride and behave appropriately!