mobs who have their generic.follow_range attribute modified seem to have their random wandering behavior affected as well, even when not following anything.
For example, use
and compare its passive behavior to that of a normal pig. It will not move from its place at all.
The base value for the attribute seems to determine the maximum distance a mob can wander in a single movement. If this is intended behavior, the attribute should be renamed 'generic.pathing_range' or similar.