I agree with the ruling.
Weidman was a victim of his own overselling.
And by that I don't mean taking the whole 5 minutes. I mean right after he took the knee he was acting like his life was flashing before his eyes because he didnt want to miss the opportunity to make sure Mousasi got penalized for what at the time was thought to be an illegal knee. Which hey, whatever. Do what you gotta do.
But then as soon as word got to him that the knee was legal he suddenly is a new man who looks like he can go 5 more rounds.
Same knee, 2 totally different reactions to it based on what he thought the end result was going to be.
That's why the fight was stopped. He didn't look like someone who could continue fighting right after the knee. He looked like a fighter unable to defend himself. So when it was determined that what made him that way was a perfectly legal strike, the fight was stopped, just like any other KO/TKO.