Agreed, however, there is a way for this not to have been a lucid dream: if your grandma told you that you are dreaming, but you did not believe her, then it would not be a lucid dream; however, if you consciously believed you were dreaming then it is a lucid dream.

I had a dream once many years ago when a dream character of mine kept telling me it was a dream, and I either did not believe it or thought that it must be his dream then (since he knows he is dreaming), right? I would not consider that a lucid dream because I think being consciously aware that it is a dream and one is the one doing the dreaming is needed for that.