It's not a "completely new theory" in the slightest. It's been well-known for quite a while that Suen's charge is what delays the casting of the second comet.
Lu'lin may be a part of the animation for the comets creation, but Suen is the one initiating it. The post you quoted isn't the first time someone has said that the charge is what causes the delay and is, in fact, correct. If Suen charges too far, the second comet will be delayed until after the Inferno. If everyone is close to Suen when the charge goes out, you will always get the 2nd comet. That's all there is to it.
Think about it from a game-design perspective: If the Ice Comet cooldown were attached to Lu'lin and not Suen, the following would be a regular occurrence: Lu'lin casts Ice Comet on player 1 immediately before Suen casts Light of Day on player one. Ice Comet is destroyed immediately without any chance of the player running away. Or, perhaps even worse, everyone is stacked up behind the previous Comet for Inferno when Lu'lin casts a second comet, knocking people out of the shadow, dealing high damage, and instantly wiping the raid.
Long story short: Suen is the one spawning the comet. If you want further proof of this, then pay attention when Ice Comet and Dusk phase line up. You'll see Lu'lin dropping an Ice Comet on a player while also standing in the middle of the room.
edit: And before anyone brings up the fact that there will be no Ice Comet if you kill Lu'lin in phase 1, I'm going to point out that Lu'lin being alive is a requirement for Suen to trigger that ability. I will also point out that Ice Comet in phase 3 is obviously an identical, yet different mechanic.