From the aticle I'm assuming that UCG thinks is is important what describes those who are part of "the Church that Jesus Built" and has a doctrine and that this would be a pretty important part of that doctrine.
So I'm asking for the UCG's (and presumably its members) doctrine here.
That's a big request. UCG isn't a monolithic organization. It's a group of people who believe in certain basic beliefs. Within those beliefs there are variations and shadows.
I would recommend starting at the www.ucg.org perhaps starting at fundamental beliefs.
A general belief, evident from reading the booklet that this article introduces, is that there is a LOT of false religion in the world including within Christianity itself. This should be evident considering especially the corruption of many "main stream" protestant denominations.
However within those organizations it's always considered that there are members of the church of God or at least potential members of the church of God.
I hope that helps/answers your question...