Definition of the word "Christian" is "of, relating to, or professing Christianity or its teachings."
From there, let us go to the fundamental beliefs or teachings of Christianity. "They are
1) the Deity of Christ,
2) Salvation by Grace,
3) Resurrection ofChrist,
4) the gospel, and
5) monotheism."
I am stressing number 1: Deity of Christ.
Following this line of reasoning, we can say that a Christian church or a Christian individual believes fundamentally in the deity of Christ. This is the foremost requirement for a person or church to fit the adjective "Christian". Otherwise, a person or a church should not claim to be a "Christian" and should be stripped of such claim. (While there are five fundamental teachings, as noted above, and to have disagreement with one strips you of the word "Christian" allow my bias on the first teaching: Deity of Christfor the sake of my line of argument.)
The Iglesia ni Cristo claims to be a Christian church, even an indigenous Christian sect.
However, the INC denies the deity of Christ. Rather, they only believe that Christ is just a mere man following or given authority by God.
Allow my argument to flow, if the INC does not believe in the deity of Christ, it is safe to conclude that the Iglesia ni Cristo does not fit the definition. Even the name of the organization is a misnomer.
To quote Michael Tan, Chancellor of UP Diliman: "Then there is Iglesia ni Cristo, not technically “Christian” because it does not see Jesus as divine (http://opinion.inquirer.net/86708/born-again)."