Yes, you can have dreams about lucid dreaming. I've done so a number of times myself, both lucidly and non. But you weren't just dreaming about LDing, your were dreaming lucidly, even if only on a low level.

Like others have said, if you decide you are dreaming then you have become lucid. However, if you only think - or suspect - yourself to be dreaming but never quite reach the firm conclusion that you actually are then you are considered to be "semi-lucid" or "pre-lucid". But I'd say you probably already had your foot through the door.