Twisted? Magical weapons dealing additionnal damages are a part of every DnD video games (and they are in the DMG). Dipping a sword in a candle is stupid and only exist in BG3.
Yup ... twisted.
Im affraid i cant explain this properly, nor i see any reason to ... in my eyes its just odd, but that is not important at all ... what matters is that you are happy with your game.

Just a question tho ...
Lets put candles aside, and ignore any other source of fire damage, even the logic that with some kind of oil it would totally be possible for short period of time ... but how about poisons?
They are also "part of every DnD video game".