Fun fact: Discord called them guilds before realising that they could compete with paid services that set up actual (e.g. Mumble) servers for you by pretending this is equivalent and free
I also have trouble going along with the doublespeak. If a supermarket called their beer apple juice, I'd also not be offering my friends "apple juice", I'd call it what it is
Guild is innocuous enough and since the API docs still call their communities that, that can be a term to use among those in the know to have common and clear terminology
'Guilds in Discord represent an isolated collection of users and channels, and are often referred to as "servers" in the UI.' —https://discord.com/developers/docs/resources/guild
This seems like a distinction without a difference. If you used a paid service offering Mumble servers that used some custom software that allowed them to offer multiple ... "servers" on different ports/IP addresses from a single daemon, would you really care?
Focusing on the fact that it's not really a "server" because they aren't running as separate processes seems like utterly silly pedantry, and we probably don't even know if that's actually true regarding Discord or not.