Flying Boat,
Just guessing, but I think the controller was probably trying to encourage you to come in 'high and tight', so you approached 'above' the flightpath of the landing 737, so staying out of the vortex, thus negating the need for 6 miles.
On the subject of the pilot sounding miffed, I've read incident reports where crews are expecting vortex separation between a heavy and another heavy on departure, but there is no such requirement in the UK. I can clear a Heavy for take off as soon as the previous Heavy is off the tarmac.
Gonzo.