Google recently announced some changes regarding its Display Network starting on January 18, 2017. From January 18, Ads and/or Ad groups with no targeting method chosen will be displayed all the way through the entire Google Display Network (GDN).
At present, ad groups with no targeting in place do not get served at all. If someone want an ad group to be served throughout the Google Display Network, than he/she have to target their campaigns by keywords, topics, and audiences.
That’s gonna change, but fortunately you should not worry about it because Google will not start serving non-targeted ads without customer’s approval.