The event in Anza did precede the New Britain earthquake. In most cases they
follow New Britain, however there may be a global environmental conditions which
triggers earthquakes in both areas about the same time, as there are a number
of cases where the Anza events precede by several hours those in New Britain.
To answer your second question, yes I think there is reason to believe that
the sequence of events in Southern California is not yet over - especially in
the region along the Salton Sea up to Anza and Yucca Valley.