No, he's talking about if you have too many units of one player being ordered, they all start to stop and move only a few units at a time.
Solution to this: Make more AI opponents and evenly distribute the enemies among them. An AI player, like a ahuman player, can only select and order 12 units at a time. When their units ordered goes into the hundreds, they cant manage all that and they start slowing them down.
-VGsatomi