Personally, I can see why he held the curtain. Curtains get held for all sorts of reasons. Having a celebrity with a large fanbase such as Rihanna at your show brings attention and publicity, which is often vital to keeping the show open and recouping an investment. If you need to hold the curtain to make that happen, then so be it. Is it fair? No, but neither are many other things in life. To me, Harris's mistake came from boasting about it on Twitter. Some things are better left unsaid, because honestly, the rest of the audience often doesn't care about publicity and will read it as a slap in the face.
The texting issue is a bit more complicated, in my opinion. The fact is, not everyone is gonna agree on proper cell phone usage in the theatre. You also can't focus on please an entire audience, because no matter what your policy is, some will always disagree (see: the thread about Yondr pouches). Harris is fully entitled to his opinion, but here is the issue that I take from it: in many ways, this isn't entirely his play anymore. It's his script, and it's largely his, but the play is now a part of a bigger production that doesn't belong to any one single person. He may be fine with the use of cell phones in the theatre, but what about everyone in the cast? The crew? If they all are perfectly grand with it, then great, but if not...well, if I were one of the actors up on that stage feeling upset (possibly even violated, depending on the scene) because someone texted during the show, and my playwright proceeded to brag about responding to her on Twitter and tweeting "miss me w tweets chastising anyone in my audience for using a phone to send a text," well, I'd feel like my playwright didn't give a damn about me.
There are a million different captions he could have put on that picture of him and Rihanna; perhaps bragging about giving her special treatment and texting her in the middle of the show didn't present the best optics. As for his later tweets about audience reactions, I don't see how that has anything to do with texting. It's an entirely different conversation.