D&D races/classes etc. are Tolkienisms, Tolkien recreated English folk lore though the Hobbit & LOTR. Elves, goblins, trolls, orks, wizards, the fay, Druids, dragons..... All of this is derived from pre-Christian/Norman English folklore. Druids were "pagans that lived in woodland", that's it. Their diet was "food". They didn't give a shit about modern day religious based dietary propagana lol.

Druidry is just as valid as a religion as any other, but is grounded in reality. Respecting the earth and it's bounty is what environmentalism is, modern Druidry. There is a 6000 year old stone calendar in Salisbury England created using this very premise. The Druids in D&D respect the balance, cycle of life and are granted powers based on what they essentially protect. Modern Druids are D&D Druids without magic powers. A Druidic diet is the bountry of the land and sea, if there are load of apples then eat apples, too many rabbits? Eat rabbits. Too many vegans? It's vegan diet time.