I am pretty sure that means does the player play to his size? Plaxico is taller than Smith, but does he outjump CBs? Reach for that extra yard? Box out CBs? I don't think I ever saw Plax do any of those. He doesn't use his size well. Smith, however, uses everything he has. I also think it works for matchups..say WR Plax 58 vs. CB Whatever 65. The CB will win in a man-to-man against Plax, but not Smith. Smith will burn that guy almost every time.
At least that is what I get out of it.