I don't think he was claiming that was the pixel size, but rather the image of a 1 micron move on the sensor, after optical magnification. But maybe I misunderstood?
That's not what I gathered from this statement:
We measured the real resolution of our system directly on the machine. We moved the cutter relative to the microscope by 1 micron and measured how many pixels it moved. The program from the camera measures pixels exactly on the camera matrix, not on the laptop screen Therefore, 4 pixels per 1 micron is a fairly real value, I'm sure of it. Of course, it could be 3.5 or 4.5 pixels.
But maybe I misunderstood. You are probably right.