The grass event did not affect lure modules, maybe that caused some confusion?
To get loads and loads of grass type, you had to walk and ignore the shiny lures.
I have also seen more grass types during the grass event in nests, and less in the places where people like to hang out around lure modules to play pokemon sit. I used the live map to go mainly for Chicorita, and the places this took me were swarming with grass types. So there was a strong biome effect, but not like you think, its the most popular spots with much lure module activity (in general, not just during the event) that got left out. You just needed to walk.... anywhere, to less popular areas or less popular nests, and you got leaf-types everywhere. Walking a kilometer for another one or two Chicoritas into some less-active area usually yielded a bunch of different grass-types on top.
This may be relevant for the next event, rock type, as well.