I'm being sassy.
But from the video, and again, nonlinear, it does appear that United, having received amended turnoff instructions after missing the first twy, simply sits there at the intersection of the runway and taxiway.
I've seen ATC issue a lot of squeezy clearances when traffic is on the runway but obviously turning off onto a taxiway, and from the video it appears that's what happened, but then United appears to have just stopped.
Again, appears. Mostly I'm just being sassy. Almost every failure in aviation safety is a systemic issue where individual performance is at most a contributing factor.