Lyricists often don't get credit when shows are mentioned, unless they're part of an established team. But the "my" in this case feels even worse - ignoring not just the other writers but the whole company that is now losing work. A simple "OUR Cinderella" would have been so easy to say.
Even wearing his producer hat. I mean, I can't think of the last time I've heard a producer say something like "I regret that we must close my production of [show]" - more commonly they'll say "our." It's just common courtesy.