If I press shift and tab the steam overlay comes up and I am also getting popup notifications inside my game window.
It's happens because game have built-in Steam support and if you got Steam client launched that use overlay and other things. But it's doesn't mean game is using Steam by any way. So lets say it's nice feature which happens because developers don't have time to build special non-steam version.
Must say, this is actually awesome. means that I'll prolly stick with uber launcher for the alpha at the very least, since backing up will make little sense with SO many updates in the near future. I wonder if it will trigger your status to say "in gameA" once the early access opens up..... (right now it just keeps with "online")