The sport band is two pieces - the bit with the holes that goes into one end of the watch and one with the fastener/clasp piece which goes into the other end of the watch.
When Apple say it comes with two bands, do they not mean it comes with one fastener end, a S/M piece with holes and a M/L piece with holes?
I've seen this done in the past with watch straps and also note how in pretty much every photo the size is only marked on the piece with holes, the fastener piece always only has the size - 38 or 32.