I think that's a point many are missing.
I could drive to a spot in Need for Speed 2015 for example, it doesn't mean that anyone playing Need for Speed could see me. Only people in my game world.
Yet people expect hundreds of thousands of people to just be online at the same time and able to see each other.
Even mmo's don't work like that, let alone an indie game made by 12 people.
Chances are there is no multiplayer at all, but the fact is even if there was then players would still be separated by "lobbies", so two random people on reddit not seeing each other isn't evidence enough, as even if there was online components to the game, it would be possible that those two players weren't in the same session.