Well if the shoe fits.
There are no rules about when you can or can't say a show was good or where you can say that and when. Stop pretending like there are.
I see no problem with what the original poster said. particularly when they didn't post any sort of review at all and just said that they saw a run through and it was good.
I agree with Mister Matt yet again. The original poster didn't even write a review. They just said that they liked it pure and simple.
Is saying something good about a show rude? Of course not. It would be rude for example if the original poster didn't like the show and walked up to one of the actors and said "if your smart you would never get on a Broadway stage in your life." That would be rude. But, It isn't rude to say something nice about a work of theatre in any way shape or form.
Just because you have a problem about this stop trying to force your opinions on other people and say how this forum should be run.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll