Oh, this. This is them predicting where you are in stealth. In Blades Edge for instance, 90% of people will just run straight up the ramp and start walking across the bridge. If you time it right you can AoE the bridge as they would get to that bit. Same in Nagrand, people generally run straight from one side to the other.
This generally stops at high rating because stealth classes start doing weird movement patterns and going different ways every game so they can't get predicted out of stealth. Another tactic is to stay unstealthed and mounted when gates open, start running one way and then stealth after about 5-10 yards, then go a completely different way and 'fake' a direction.