If I understand your question, consider: A pixel (picture element) is a discrete entity, not a unit of measure.

A pixel, like a "dot", can be any physical size. The number of pixels in a measured unit determines "resolution", usually expressed in "ppi" (pixels per inch), which could be translated to pixels per meter of resolution if need be. For example, a computer screen may represent 96 ppi (96 pixels by 96 pixels = 1 square inch) resolution, yet for printing 300 ppi (300 pixels by 300 pixels = 1 square inch) is common.

The number of pixels in a meter, therefore, could be 1 or it could be 1 billion. Apples vs oranges.

I hope that makes sense to you.