A-ha, your new video shows something that .. you indeed already mentioned in your original post (sorry): you are working in pixels.
(Healthcare warning: OT Rant follows.
Please don't do that. Pixels Are A Lie. The size of your pixel is different from mine, and from just about everybody else who doesn't have your monitor and your graphic card and your personal screen resolution selection. Your pixel may very well be rectangular or hexagonal!
I've lamented the inclusion of "pixels" to InDesign right from the start. Ever since befuddled professional users have cried why! why! and befuddled newcomers wonder why InDesign's pixels are somehow "different" from those in Illustrator, Photoshop, Microsoft Paint, PNG images saved out of InDesign, and HTML browsers.
/End of OT Rant)
This appears to be a hidden feature of InDesign: as soon as you indicate you want to work in pixels by setting your rulers to this, the Pixel Grid automatically jumps into action. And you cannot switch it off, presumably because Adobe reasoned that "that is after all what you want if you are going to work with pixels": there is no practical "half-pixel" or smaller unit that you'd be able to use, as it goes against the practical use of "pixels" as a unit!
Quick solution: switch your rulers to a more stable, Real World measurement unit.
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