Are these ground stitching vias? If so, why are they placed in this manner?
Yes, they're ground-stitching vias. You might also see similar patterns for thermal conduction, but that doesn't seem to be the case here.

Did they go overboard or is this crucial to have for good signal?

There are probably more vias there than are strictly needed, but a few extra vias is cheaper than a board re-spin.