I assume there is a copper pour on the top as well, and the bias are stitching the top and bottom planes together. Depending on the frequency of operation, it is possible that the via spacing would help to cancel out emissions. But in this case this effect would not be significant.
What I find interesting is the different via spacing and sizes in the input and output sections of the board. These must be significant, probably contributing to impedance coupling or simply filtering. I’d be curious to know the relation between via spacing and wavelength in those sections.
Of course, these could also be attachment points to simplify test setups. You might be able to get a straight answer in the manufacturer’s forum.
In low frequency boards, you would find prototyping sections that look very similar, but that is clearly not the purpose here.