Apple Preview - 100% image scale displays as 200%?

I have a 5120x2880 image. That resolution exactly matches the resolution of my 27" iMac (currently set to "Default for display" under the display preferences.

Most image apps I use, when displaying this image at 100%, fill the screen exactly, with 1 image pixel to every 1 physical screen pixel. This includes Capture One Pro, Affinity Photo, and XnViewMP.

Apple Preview, in contrasts, when set to "Actual Size", displays the image at what looks like 200%. Note that I have the Images preferences set to "Define 100% scale as: 1 image pixel equals 1 screen pixel:

I'd have expected that setting to fill the screen exactly, not double it.

So: why is Preview doubling the size of the image? Does it not handle the Retina display the same as other image apps? Any insights appreciated.