My understanding of the terms is that track is a fully produced song, ready for publication. A songwriter can write a song, a singer can sing it, but it's the producer who makes the "track."
I've heard it most often as industry jargon, I wouldn't chastise your friends for not using it. A "song" without words is more typically called an "instrumental."
Of course different genres have their own terms. A classical instrumental is often called a "piece." I wouldn't be at all surprised if the "correct" word within the subculture of dubstep fans is track. If that's the case, however, you're unlikely to find any official support for your position, since the rules for its usage are almost certainly unwritten.