Hey,
Actually it's perfectly normal to have a lucid dream without the need of practice..
I myself have been fascinated by dreams ever since I was a young boy...I've had 2LDs when I was about 7-9yrs old...
At that time,I thought that there was no way of controlling dreams,and that me realizing I was dreaming was purely coincidental...
So,yes its normal to have LDs without practicing...my friend had a Lucid Dream after watching Inception and she barely knew about Lucid Dreaming...
Hope it answers your questions,
Sam