Facebook updated their status

Hi,
I keep getting these Facebook update messages in my email inbox. "Arnold updated their status". Shouldn't that be "Arnold updated his status"? Considering billions of people are receiving these updates, I think they should be grammatically correct, or they might start a new trend. Or am I wrong?
Thanks,
Andy
You are not wrong just by the fact that you have to raise the question.
It just so happens that I agree with you. Β (Though this usage has been quite common for quite a long time.)
"Singular they" is now entrenched. You can't say User @grumpycat updated his status because @grumpycat might be female (the internet celebrity of that name certainly is) and you can't tell with absolute certainty from the name alone. Any given Facebook account might belong to a man, a woman, or an organization.
If you don't accept singular "they", you'd have to insist on "User @somethingorother updated his, her, its or their status", which would become even more annoying in very short order.
It is entrenched but in a very limited domain (namely that of impersonal references). Β If you don't mind pub parable by way of illustrating that limitation:
Guy lames into a bar, all tears: Β Buhuhu ...my wife wants a divorce!
Bartender: Sorry to hear. But on what ground can that be? Β A super husband you are.
Guy (both hands in the air): Β On ground of irreconcilable English, of all things !
Bartender: Β Wha..what in the world can Β THAT Β be? Β Your English is super articulate and super advanced as is!
Guy: Β I can't figure. Β I ask them to explain, but all they does is rolls up their eyes! Β Buhuhu.