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.