Footage from my 1D Mark IV is showing up, in explorer, as 23 frames per second. When I import those files into my timeline (23.98fps) it asks me if I want to change the timeline settings to match the clips. Now I'm confused. This has never happened. Any thoughts/ideas?

what matters is how it shows up in your NLE. Maybe explorer is not looking at the full number. Try another test with maybe 29.97 (30p) and see what explorer does.

That's the thing...but I might have found my answer.

I was using the HDV preset in PP. I'm not sure what the exact differences they are to the Canon DSLR presets. I know the fps is the same. Anything else that might prompt the NLE to ask to change settings
of the timeline to match the clip?

I put the file on a Canon DSLR preset and it worked fine.

ETA: Looking at the preset descriptions, I think I 'may' know why things weren't working well.