It means that guy is much much fitter than you. the issue is not whether a short guy can beat a tall guy, it's about the extra work a short guy has to do to cover the same distance in the same time as the tall guy. at the end of the run say 5 km, the shorter guy would be tired out more than the tall guy cause his little legs were moving twice or so the speed as the taller guy. Whatever size you are, if you do say 100 punches in a minute then next tried to do 150 punches in a minute(after a decent break), which one would tire you more???