Not surprising at all. Conventional layout wisdom says give the eye a clear path in a direction it knows.
A multi-dimensional grid takes you in a Z shape, whereas a vertical lineup's images and text are all aligned and easier to distinguish.
A multi-dimensional grid takes you in a Z shape, whereas a vertical lineup's images and text are all aligned and easier to distinguish.
I think I'd overestimated "pretty" and underestimated "functional" in this case, so the results were a wakeup.