Clearly, you don't have much knowledge in engineering, especially in civil engineering. How could you assume the brick is exactly is 5x4m, the process for you to get those numbers is pretty unreasonable, based on " relatively standard ", what standard? Like I repeated many times, it's a construction material, I won't be surprised if their error to be more than 10cm differences between each. And if you won't read what other people wrote then, I'm done discussing this with you.
Also, more importantly, known how runway is constructed, those are not actually "brick", normally they will do the entire runway in concrete and after the concrete is dry, they use some machine to cut out each channel for the concrete to be able to expand in the summer and shrink in the wintertime. And if you have any idea about the civil engineer, trust me, their minimal error is measured in cm, whereas 1mm (mostly even much less) in jet production.
So I will say your pixel measure will be much accurate than the grid approximation, just need some additional error correction to get the estimation more reliable.
Brick was the term you used. I actually assumed these were concrete blocks. If your point is that there's divider lines, well, it's notable that they seem uniform with a 5:4 length / width ratio. At the scale of the picture, likewise, 18 pixels = approximately 1 meter if we assume 5mx4m, perhaps 16-17 pixels = 1 meter. A cm error wouldn't be visible in that picture.
Measuring different square units, it seems as though the rectangle size is uniform.
Also, I'll point out that this is a military runway and therefore can't be expected to be built similarly to civilian runways. It, in contrast, has to be hardened against explosives (because explosives will be used against the runway) and be built in such a way that mines laid onto the runway to impede repair can be easily removed.
Here's another shot of PLA runway material.
Christ, are we now discussing pavement?
An old introduction to airfield pavement: