By your argument, League of Legends, and the whole MOBA genre, would be as much PvE as they are PvP. Much of the game, after all, is killing NPC minions.
Using the term PvP to refer to a game mode, server, game, etc that allows both PvP and PvE is the common stance in the industry. Look, for example, at what are called PvP servers in most MMOs; they are normal servers as far as PvE availability is concerned, but atop that allow PvP to happen. Hence, by having both PvE and PvP, they are called PvP servers, in contrast with the PvE servers where all PvP is either removed or made optional.
Consent is the basic difference. You can PvP in Mobius, but only in a way where every player must actively choose to engage in PvP. The same way, in other MMOs, game servers that only allow PvP by mutual consent are called PvE servers.
Of course, Mobius isn't a true PvE group because the devs didn't provide us with the tools to completely prevent unwanted PvP. Which is a flaw we really want fixed, preferably by adding a true Open PvE mode, though merely providing the tools to disable PvP in a group would already be a great help.