The way I think of it is that from NIS 2012 to NIS 2013 is in fact a version upgrade, while from NIS 19.9.0.9 to NIS 19.9.1.14 is a version update.
IMHO this setting is in fact misnamed in that it should say Automatic Download of Version Upgrade. As in an upgrade changes the main v # from 19 to 20, while an update changes the v # within the main v#. ie 19.1 to 19.2 etc.
I have seen some confusion from users where they said the version number changed even though I had selected not to Automatic Download of New Version. In these cases the version number changed within the mainv # as explained above.