well, you might have been.
did you get a sudden moment of clarity, where you thought 'i'm dreaming' and go from there?
i usually get some indication that i'm dreaming, i don't just switch seamlessly from non lucid to lucid, something gives it away usually, an odd occurence, or a sudden desire to do something, for example, i had a lucid dream last night, and decided to make someone disappear.
hope this helps.