Now, I know some people think "Online game sounds bland, that is not sexy at all. Lets call it MMO, that will make it sound much cooler!"... its ridicolous when big studios do it (World of tanks a MMO? Don't make me laugh! A persistent player garage and stats and a chat lobby does not make an online game a MMO! Does not make the game any worse to play, but the marketing surrounding it makes me chuckle regularly)...
If small startup devs like you use the monicker, its even more ridicolous. MMO might not be as clearly defined as RTS as a genre... but its pretty clear that not all online games are MMOs.
In fact, the first "M" stands for "Massively", and is the reason why expierienced devs will tell you that the expenses and time needed to develop an MMO is just as "Massive".
I shouldn't actually trap myself in a discussion like this but MMO is apparently heavily opinion based like the term roguelike, nowadays people and devs easily tag there game roguelike while it has absolutely nothing to do with Rogue . But why does world of tanks should not fall under MMO? Should eve online be defined as MMO? Each system in eve has it's own instance and starts lagging with 100 people in it. Basically everyone in eve communicates over a simple chat box like in world of tanks and direct massive player interaction is minimum. Yet the player counts are massive for both games, both are multiplayer and both are online. Massive does not say anything about visual content or how player interactions should be., that is what you are making up yourself I guess. Hack, for all I care candy crush saga is MMO, all my friends compete for the highest score so it even has the grinding of a MMORPG .