Would you still be Christian if the Muslims set up the date system and based it on the birth of Muhammed?
The year they estimated is off, meaning that Jesus was not born in 1 B.C, but actually born somewhere around 3 B.C.
Non-Christians didn't like that their dating system is based on a religious figure and so they decided to rename it C.E, common era, and B.C.E, before common era. I still prefer to call it A.D. and B.C.