I'm very wary about supporting developers/publishers who use always on drm, so I do my best to research what drm is in the steam games I want to buy. When looking at the system requirements, some games say "Broadband Internet Connection" with no other qualification. Is that for multiplayer? Or is it a drm? Take for example Mortal Kombat Komplete.
Sometimes it's for multiplayer in the case of MMOs and similar games like DoTA 2. Other times it's for DRM. Mortal Kombat Komplete appears to be one of those kases. It appears that most of the DRM list are activation checks and you don't need to maintain an internet connection for single player.
Since that's written by the publisher, there's no sure reason every time, but usually that does refer to online multiplayer. It could refer to DRM as well, but that would usually be indicated on the page as well. To make sure, you can always check The Big List of 3rd Party DRM on Steam.