I was thinking about this on the drive home last night, and I think you're right.
Some of the newer kegs I have also have a venting bung. The bungs are black with a red middle piece. The middle part (spile) of the bung is had a flat side to it and the black bung has a vent hole in it which is marked, I think, with an arrow.
If you turn the red piece to line up the flat side with the vent, it's designed to open a vent which releases pressure and allows air in for a smooth pour.
This is probably exactly what you're doing.
I also have one of the counter-top Beertender things, which pumps air in to push the beer out. I suppose this could also work for cask conditioning, in that you're not pushing with CO2. I've only used it for parties where the beer is gone before the people are.