Absolutely, the whole movie felt like that which was a big part of it’s charm. Watching the first scene I could imagine the players asking the arrakoan chancellor’s name, which the DM hadn’t prepped, so he just made up Jarnathan on the spot…
The fat dragon, Themberchaud, is actually a canon obese dragon. He’s in the Out of the Abyss module and some others.
That freedom is exactly what I like about ttrpgs too. How do you do it solo?