For some strange reason, GOG likes to make up their own numbers for the installers, instead of displaying the actual version number of the game. I think GOG labels it "1.6.0" because they have updated the installer 6 times. Anytime a game gets an update, GOG increases that game's installer number by .1.
I have no idea why they do it this way - it just confuses everyone.
It is incredibly annoying in modern games.
If I had to guess why they do it, its because they started out with ancient games which they had to work on to make even run on a modern OS.
so the game version is always "the latest version from 20 years ago" but the gog version number indicate changes to the installer / compatibility fix pack they apply to it (usually dosbox)
Now that gog is no longer exclusively dealing in old game, they should introduce an alternative system to new games where they give us the actual version number