He doesn't need to chain, the Grassland is adjacent to the River (oh see which one you are talking about)
BTW, the Black Circled +2... is that Actually a Grassland tile?, or is it a hill with a food resource?... or does it not actually give +2 even with Bio. O wait, thats The proposed city spot...
So 5 bonus food Pre-Bio =2 Gold, and some slow growth (into farmed Plains+Windmilled GHills which are self supporting)
12 bonus food Post-Bio = 6 Gold, and pop stops
a Good slow Growing, Decent production Super early Commerce City.
It can reach size 13 (with 2 Golds) prebio, and then grow to 17 to get the other 4 Golds post Bio. Most tiles, except the Floodplain+Grassland, would give at least 1 Commerce and 1 Hammer