It's not. After much discussion, the StreetComplete team have decided that pubs and a few other places won't ask their dietary quests unless food=yes is tagged, hence the note to get this added: https://github.com/streetcomplete/StreetComplete/blob/0435965da1e25f85f18720d4737e9753f98fb566/app/src/main/java/de/westnordost/streetcomplete/quests/diet_type/AddVegetarian.kt#L20
and
https://wiki.openstreetmap.org/wiki/Tag%3Aamenity%3Dpub and https://wiki.openstreetmap.org/wiki/Talk:Tag:amenity%3Dpub