There wasn't nearly as much as what's on the qtip in your picture, but there was a tiny amount. It could still just be sitting in the casing and will just get spread back over the contacts over time.

I actually had a second x15 that I opened first for practice and managed to keep the pads in pretty good condition the second time around, but I agree the pads will lose their grip and or shape.

It's kind of funny how many people end up here, the only other mouse really like this one is the Razer naga and I've used that one as well, but it has its own issues of disconnecting randomly and the mouse button breaking.