That's probably not really anonymous - Quora almost certainly knows you posted it still even if they don't display that you did.

Correct, Quora does know that you posted it, however other users won't be able to know:

http://www.quora.com/How-anonymous-are-anonymous-questions-i...

For now. It would be a mistake to assume their system is so secure now (and forever into the future) that the data can't be found, or simply leaked inadvertently by Quora.

Or forced to be handed over with a court order.

It's a very false-anonymity, even by internet standards.

I agree with you, and I have also posted this question on Quora which remains (to date) unanswered:

http://www.quora.com/Have-Quora-admins-ever-unanonymized-a-q...

Yep, of course, but often that is enough.