It was believed that an "Anti-Christ", who was suggested as being a devil, was to indicate the apocolypse, from my understanding. Some (maybe most) religions believe an "Anti-Christ" may come, and fear that possibility. (Perhaps an elaboration of Kiwilady's comment)
As may have been mentioned before, Christians are those religions (or individuals) who believe in Christ. Catholics, would be more of a specific type of Christian, but even that has another large catagory (i.e. Roman Catholic, Orthodox Catholic, Eastern Orthodox Catholic, etc.).
In my studies of Catholosism in my Roman Catholic Church, I heard nothing said about an "Anti-Christ", but was told "Jesus Christ will come again".
This is based on recollection, so someone may either correct, agree, or expand on my opinions.
But, I'd have to agree with Lilith, the person stating they were a part of the Anti-Christ, was either a devil worshipper, former Christian who hated that religion, or of some odd deviation from a Christian religion, most of us are un-familiar with. (Now, if they said they were a part of "The Body of Christ", that would be a totally different statement!)