There is a link to the full video at BroadwayWorld. I don't think the Variety article accurately depicts the situation. It's pretty clear from the full remarks that what Lloyd Webber is referring to as a "costly mistake" is re-opening the show too early in the pandemic. Neither the cast nor the audience react much to "costly mistake." What gets him the boos is not having shown up in person. After the boos, Connor implies that Lloyd Webber has a very good reason not to be there but stops short of saying what that reason is.
What I find interesting is that Connor says something along the lines that he isn't sure that Cinderella is going to have a life beyond that closing performance. If the Broadway transfer was set in stone, I don't think he would have said it in quite that way.
