The sentence "Steam doesn't enforce DRM" has only one valid meaning, that Steam the platform doesn't require you to have DRM to be on it.
The alternative, that Steam DRM is used but doesn't actually do the thing that DRM is supposed to do, ie prevent copying, is nonsensical, and thus can't be what OP meant.
Therefore, we are forced to assume that they meant that "non-enforcement" means that Steam the platform doesn't require DRM for your game to be on it, which is true, it doesn't. That's the only reasonable interpretation.
