Are iPad my videos actually ON my iPad?

Because they don't seem to be.  Most of my video content gets to my iPad via a file browser app.  I create, edit, trim, etc, the video on my PC then use the file browser app to C&P it to the iPad's camera roll.  From there I can insert them into Keynote presentations.

 

Today I happened to be in an area with no internet access, so I couldn't even use my phone as a tether.  To pass the time, I opened up the videos folder (within the photos app) in the iPad.  To my surprise, all I got was this when trying to play a video:

 

 

How's that for an informative error message?  Apparently, videos which I have previously imported to the iPad's camera roll still require an internet connection to play.  That means they're not really on the iPad; they're being fetched from somewhere (iCloud would be my guess).

 

Later when I was back in WiFi land, I opened the video and it played after a few moments of hesitation.  Then when I tried to edit the video, I got this:

 

 

I guess that confirms it.  Videos aren't stored locally, even those I've physically transferred to the iPad.

 

Okay fine, the iPad is backing up my videos to the cloud.  I get that.  Thanks, I guess.  But I want them stored locally, too, for times when I don't have internet access.  That's why I put them there in the first place.

 

Now I know why videos take a few seconds to start, and if I fast forward, the video hangs again while the download jumps to the new starting point.  Can somebody tell me how to force the videos I copied to the camera roll to actually stay on the camera roll?

iPad Air Wi-Fi, iOS 11.0.2, null