FireTV/Kodi - can you watch movies from a flash drive without internet connection?

Hi there,

I have an Amazon Fire TV box (and some sticks too).
And I use Kodi with it to stream video.
And I've also been able to play some movies that I have on a USB flash drive.
All good; I love it!

I then thought I'd be able to take the little Amazon box on holiday with me, and watch some movies from flash drives by just connecting the Fire TV box to the TV in the holiday cottage.

However, it didn't seem to work. I couldn't seem to get past the obstacle that there was "no internet connection" (cottage is remote with no internet).

My assumption had been that the video player software was installed on the Fire TV box (whether Kodi or the Fire TV software itself), and that the data (the movies) were on the USB drive. Therefore, no need to require an internet connection.

Is that assumption completely wrong, or is there some way to use that FireTV/USB setup to watch movies with no internet connection in place? Is there some setting/process I should adopt in such situations?

Many thanks for any pointers/advice you can offer,
Richard