My understanding is that it means rund = beef. The words are similar (in my mind) to the German.
Fleisch which means all meat (chicken, lamb, pig, beef) but Rindfleisch means beef, Schweinefleisch = pork, Hähnchenfleisch = chicken meat. Fleisch and vlees to me sounds like flesh. That's how I remember it. cow flesh, pig flesh. etc..
beef = meat from a cow/bull/ox (http://www.oxforddictionaries.com/definition/english/beef)
So if you say beef meat you're saying rundvlees vlees.