I'm not sure what to think on this one. This can definitely be discussed without lying to ourselves though. He did not slip. He went down to avoid a hit.
I also am not buying his story that he thought he had it. I hope that Tyler is enough of a pro at this point in his career to know where the line to gain is on a third down. And, he went down well before the line.
If he hadn't gone down, would he have picked up the yardage? I don't know. Tyler is a lightweight WR and he had 4 DBs in front of him. On the other hand, his momentum was in the direction of the line to gain, often multiple defenders converging will result in a seam for the ball carrier since they cannot occupy the same space, and the defenders were not squared up. I doubt he picks up the yardage for a first, but no way to know for sure.
Tyler is making business decisions this year. I'm not saying it's right or wrong, just acknowledging the truth.