
Thank you! I thought that it was just an oversight but I was just curious. And yes I was reffering to the movies. Thank you!If you’re referring to the movies (which it sounds like) it was most likely an oversight and poor script writing.
In the books, which are canon, Thorin was born in TA 2746 in the Lonely Mountain. They fled in TA 2770 so would all have been well aware of Smaug and what he was.