If they want to say they are Christian, let them. They usually treat the word "Christian" as a dirty word.
Christians are an offshoot of Judaism, just like Islam, JWs are an offshoot of a Christian sect. It is like a copy of a copy of a copy- not a good representation of the original. In this case, it isn't even a good representation of any of the copies.
Unfortunately, it was the love, kindness, charity, and social responsibility that was lost in all of the 'splits' so the JWs are left with nothing good. It is hard to find a religious group that has no redeeming qualities, but here they are.