Grasses mentioned in the article: rice, wheat, maize and sugar cane. I think all of them likely beat the bamboos because there are too many different bamboo species, not a single dominant one.

That's not necessarily grasses though. Rice is a Poaceae, https://en.wikipedia.org/wiki/Poaceae, so these are covered by the grass family - but grasses would be the non-eatable variants in the wild. See Wikipedia:

https://en.wikipedia.org/wiki/Grass

"The three major families of grasslike plants are true grasses (Poaceae), sedges (Cyperaceae), and rushes (Juncaceae)."

So he at best only did the family Poacaea but where are the wild poaceae in his calculations?

Tons of things are missing in that article.

The wild Poaceae have a many times less mass than the cultivated Poaceae and than the most abundant trees. That is why they are not mentioned in the article.

TFA is correct that among terrestrial animals only termites and ants have a biomass comparable with humans and domestic animals, and among terrestrial plants only some of the most abundant trees have a biomass comparable with the principal cultivated plants.

Trees are favored in this comparison because most of their mass consists of relatively inactive structural organic material. If they had an inert mineral skeleton, they would have contained less organic substance than the main cultivated plants.