I find this quite interesting, it's a focus of the game at the moment that slow play is an issue, here you have someone trying to keep the speed of the course up (although appreciate in a very poorly delivered way) and the response is annoyance at him and a report to the manager.
Pro on the other hand just tells people the course is playing slow and that's fine.
You don't want to be firing balls at the group in front, but maybe he thought that by backing off you weren't in a position to immediately play when they left the green. No big deal if you're relaxed about it but if all on the course were doing this then perhaps it could significantly slow the pace over 20-30 groups.
In agreement here. maybe the guy didn't handle it in the right way, but if you don't keep up with the group in front and an opportunity to play though arises you can't take advantage.
its quite common, its slow ease back, which only makes it slower for those behind.