Why is people in Antioch were first called christians were in fact they are pagans?

Answer 1

I know that Antioch was one of the first cities to be visited by apostles, notably Paul, who established house churches.
Here is a quote from wikipedia:
Founded near the end of the 4th century BC by Seleucus I Nicator, one of Alexander the Great's generals, Antioch was destined to rival Alexandria as the chief city of the nearer East and to be the cradle of gentile Christianity.

Here is another quote from the same site:
Evangelized perhaps by Peter, according to the tradition upon which the Antiochene patriarchate still rests its claim for primacy (cf. Acts xi.), and certainly by Barnabas and Paul, who here preached his first Christian sermon in a synagogue, its converts were the first to be called Christians (Acts 11:26).

They multiplied exceedingly, and by the time of Theodosius were reckoned by Chrysostom at about 100,000 souls. Between 252 and 300, ten assemblies of the church were held at Antioch and it became the seat of one of the four original patriarchates, along with Jerusalem, Alexandria, and Rome (see Pentarchy). Today Antioch remains the seat of a patriarchate of the Oriental Orthodox churches. One of the canonical Eastern Orthodox churches is still called the Antiochian Orthodox Church, although it moved its headquarters from Antioch to Damascus, Syria, several centuries ago (see list of Patriarchs of Antioch), and its prime bishop retains the title "Patriarch of Antioch," somewhat analogous to the manner in which several Popes, heads of the Roman Catholic Church remained "Bishop of Rome" even while residing in Avignon, France in the 14th Century.

Answer 2

The Apostles were first called Christians in Antioch, not the people of Antioch.