Colin, I have found pretty much the same info. What I can make of it is that "Adaptive display" changes the display's power saving for specific moments and others relatively close.
i.e. I'm studding an architectural design for a long time. Then the screen turns off, but I'm still reading the same plans. So, I move the mouse a little, the screen comes back on. Now, the computer thinks, "Hey, he's really is still there. I'll give him an arbitrary amount of more minutes on top of the predefined minutes in the 'Turn off display after' setting."
From now until the next time the screen turns off is "Turn off display" + "arbitrary value" minutes. For every time this repeats, the computer adds more minutes until I don't move the mouse. Then the computer gets to think, "Good, he's gone. Now I can take over the world!"
OK, maybe that last part doesn't happen and it just resets to "Turn off display"'s value, but hopefully you get it.
What the random amount of time actually is, we'll never know until someone trial and error
figures it out, or Microsoft talks. That last part makes me sad, because, I too, wish most of this stuff was annotated with actual definitions.