It seems the survival meals from the default start rolls random veggies for vegetarian. These are able to be made of raw fungus. Since the starting survival meals are usually created to be made out of the food that your people want/need (human meat for cannibals/meat for cannibals etc.), putting fungus in it when not being tunnelers seems to be an oversight.
Fungus meals: https://steamuserimages-a.akamaihd.net/ugc/1841409829039363046/8D94A92A79D3B71F83C3032AC80B9CBED5488F77/
Ideology combo: https://steamuserimages-a.akamaihd.net/ugc/1841409829039363382/125311164AE6E5F41303A13DDE1180AEC4304260/
Both DLCs, no mods used.
This might be intended because that's the hand RimWorld sometimes deals you, but I will double check if its intended or not with the devs. Thanks for the report.