When he said: "Neither of us knows, both of us believe."
How is that automatically an affirmation of doubt?
But, the definitions of these faiths are incompatible. Jar may well be a Xian, but his flavour of Christianity is incompatible with all known definitions. Perhaps Jar's definition is correct and every other 1500 plus denominations of Xianity are mistaken.
The 1500+ denominations of Christianity also believe that the other 1499+ denominations of Christianity are somehow wrong with regard to some or another subjective detail of the religion. All the specifics you are bringing up I could easily do from another perspective. From the penecostal perspective I could come and say that Jar's belief is not compatable with Christianity because he makes no mention of his infilling of the holy spirit evidenced by speaking in tongues. The only thing that is differet with you is that you are taking the subjective points that happen to be major threads in the some of the mainstream formal Christian denominations. Certainly some flavors of Methodists might disagree that there is only one right way to God. Other may have varying flavors of what is considered "saved" or not saved. Jar didn't mention his baptism. According to another major thread of most mainstream formal Christian denominations, if he is not born again of water then he is not saved.
Where do you draw the line? You seem to be putting forth a sophisticated "no true Christian" type of argument.
Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)