Heart of Darkness said:
If you find a bug but leave it in,then it's not a bug, but a feature.
I was going to say something a lot like this. A bug can basically be anything that wasn't originally planned. If all enemies have 50% more health than they're meant to, that is a bug. But if it turns out that this is actually better for the game, it becomes part of the design and they leave it in.
It would have been nice if they gave an example of what they meant though. I'm totally cool with things like I just mentioned where they basically stumble upon good ideas. However, if they mean "it's funny when you fall through the ground if you stand in this particular spot" or there is some other real kind of glitch, I'd prefer if they'd fix it.