In the spirit of informing future readers, you flipped your calculations. To fill a full-frame sensor with a 5mm object would require close to 5x magnification (24mm/5mm), and a crop sensor would require 3x (15mm/5mm).
So getting a good close-up photo of a 5mm object very much requires a macro lens, and even a standard 1:1 macro will not fill the frame, although having some space around the object for context is not a bad thing. Something like the Canon MP-E would work better for extreme close-ups.
I agree that the vast majority of the images in the OP's link were not macro, and could be taken with a normal lens, although a few are borderline macro (like this one: https://www.instagram.com …0G2djERX/?taken-by=kalpay) depending how large a sensor was used to capture the image
oh oh oh