Yeah, not sure what Rumble was thinking with that strategy. I can understand throwing in some takedowns into his striking to keep DC guessing and hopefully setting up a big strike, but just purely trying to out wrestle him?! Foolish.
The way I saw the Mousasi Knee was that Gegard was the one who picked Weidman's second hand off the mat because he knew that had both hands been down it would have been illegal. However, due to the ref's angle he could not see the second hand and for some reason decided that meant it must have been down and therefore the Knee was illegal. When the ref asked Weidman if he was ok, Chris was an opportunity to try to cheat and get a rest (he was clearly gassed) so he pretended he was hurt more than he was. When the ref saw the replay and realized the Knee was legal Weidman's trickery backfired on him and the doctor called the fight believing that Chris was badly hurt and unable to continue fighting.
Weird ending/stoppage though no doubt.
Personally I think they should just completely do away with those "no knees to the head of hands are down" rules altogether. If you want to avoid getting kneed in the head, then either defend it, or change your position so you aren't in a position that is open to them anymore. No more rules that protect or foster "fatal tendencies."
Just my opinion though.