Without seeing it & going off your description and what i can recollect, sounds like Cooks had a tight split (based on being in between the left hash & numbers) & the route was a post corner & the browns were in some sort of zone coverage.. 4/6 look. Hard to know exactly without seeing it & knowing where the TE was. WR's are taught several things in order to create separation. In this instance i think Cooks faked Mills out on the "post" portion of his post corner route b/c when he broke inside towards the safety and began attacking the safety's leverage, to get him to slow up and/or widen, he held it for a tick longer than normal before he stemmed & broke his route back outside. Mills probably thought Cooks was gonna continue inside & threw it that way just as Cooks was breaking outside. So the screw up is probably on Mills.
Again going off your description it only makes sense for Cooks to break his route away from where the defender was..in this case the safety who was the only defender in play. Which leads me to believe it was likely a cover 2 look disguised as man..or something else. Reason i believe this is b/c the holes in that coverage are in the seams between the mlb's and safety and that deep outside 1/2, the later of which is where Cooks was probably breaking to.
Close.
It was a 3-4 zone.
The Texans were in single back, double TE set, with two receivers on either side.
Cooks (the X) simply runs a seam route while the other receiver (the Z) runs a crossing route underneath him. It was just a two-man route; the other 3 skilled players were basically at home to block/draw the attention away from the LBs.
The crossing route by the Y, from my understanding, is to try to draw the FS up, leaving Cooks alone in one-on-one with the RCB.
As it was, the FS never bought the shallow route and stayed home.
This, IMO, should tell the QB to either go with the corner route to the X or the shallow crossing route by the Y (depending on the depth of the RCB).
We see this route a lot, not just with OB, but with other teams, and at the collegiate level, too.
The fact that Cooks started to turn to the outside to look for the ball was also telling.
He was expecting the ball to go to the outside.