Are Christians who question the authenticity of modern day bible(s) or the notion of Trinity considered "Ahlul Kitab"?

I know someone who was raised Christian and continues to believe in God, but questions the modern day bible and believes it to have been altered, he also questions the notion of the Trinity, and whether Jesus was simply a human and not is not to be considered the son of God. My understand is that what defines "Ahlul Kitab" are that they believe in God and believe and follow the guidance of the bible/torah based on them being Christian or Jewish, but in situations where someone questions the modern day version of the bible and believes it to have been altered, is he still considered "Ahlul Kitab"? Thank you