BeamNG.Drive does not require Steam to be running to be launched, which shows that it does not use Valve's DRM system and as far as I can tell, no other DRM system is in place on the game even if you buy it from Steam. There are plenty of people on Steam who dislike DRM. So why not mention it on the Steam page?
I'm not sure it would be true.. You still need to install and run Steam to download and update the game. The Humble Bundle version is marked as DRM-Free, as you can download from HB without having to install any client and similar.
So to update the drm free game i have to have it installed on steam aswell? Cant just download an updated version from humble bundle?
If you purchased the game from Steam, you have the Steam version, which requires Steam to install and update it (no Steam game is DRM-Free, as you need Steam to be able to access them in a way or another) If you purchased the game from Humble Bundle, you also get the DRM-Free version, which can be updated by simply downloading the ZIP or Installer from Humble Bundle https://wiki.beamng.com/Updating_the_game