The key word is definitely performance. But people generally don't call actors liars for doing their job.

One should not pretend that social media is a place to broadcast your unedited inner-most feelings. It's media. Even if you are honest, it doesn't mean you're good enough at expressing yourself that what you intend to come across actually does. If you don't feel you'd be confident expressing yourself millions of people on prime-time television, you shouldn't feel confident expressing yourself to millions of people on twitter.