Seems like it is the developer's location, with the following note from the bottom of the link:
"(However, there's still the caveat that if any app triggers “Snap to Road”, all apps get “Snap to Road”.)"
which seems to be a poor implementation decision vs providing apps snapped or unsnapped location data based on their setting, but may be the result of some early-on ill-considered internal designs?
If the app developer in turn wants to allow the user to modify that setting, then more power too them.