might be the installer you downloaded, the first download option has galaxy with it

As masterian said, this is no DRM. It's one of the more criticised moves from gog "to make galaxy more accessible to the masses", but it's closer to the crap that java installer pulls (you don't pay attention you get a browser toolbar and/or antivirus you never asked for).

You can still download something called "classic installer" that contains no traces of Galaxy, but you have to explicitly select them from the "More" menu.

You can go into your games library click on GrimDawn, then click on the "MORE" button, in the drop down menu click on "Settings".
Under the "OVERIDE FEATURES" uncheck "Display Notifications and access GOG GALAXY when in game".
That should shut off Galaxy access when starting the single player.

I do agree that it is kind of a sneaky way of getting you to use Galaxy.

But if you uninstal galaxy you can still play the game right? You dont need to redownload game normally?