Generally mods are derivative works meaning that you infringe on the copyright of the original product. Afterall, your mod requires the original work to function and you build on top of it.
Nothing you produce for bannerlord is entirely your own, assuming you're using TW API. It's like if you took a painting and painted some more on it.
IANAL but such things tend to be covered by EULA of the game itself. Since there is no official modding support and no official modkit this is probably all up in the air.
My guess is TW can take your code and do whatever they want with it considering that it is derivative work, but they're unlikely to do so. You are most likely free to reuse your code and ideas too, as long as you unplug them from their API.
Can they take your work? Probably. Are they likely to? No. There is no history of them doing something like that, and to my understanding they preferred to work with the community keeping up good relations.
Personally, sorry about the jab, but I think it's laughable how protective people get over their mods. If they took my code and plugged it into the game I'd be honored.