I would say that's an unhelpfully misleading statement in the license.

There exist obvious circumstances of the program's use with which the license doesn't concern itself, and does not speak to, and so in those circumstances the user is not required to enter into the license.

A redistributor must enter into the license because it's a derivative of the GPL, and so it has requirements related to distribution.

A user who runs the program in such a way that visitors communicate with it from remote stations obviously is required to enter into the license also and comply with its requirements.

The license is applied to programs for which this would be a typical use.