In John 14:6 Jesus said, "Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me."
For a Christian to say that there are other ways to God would be for them to call Jesus Christ a liar. Since true Christians don't do that, they tend to believe that everyone who thinks that they can get to God without Christ as being deceived and on their way to a place that is very different from heaven.
The Apostle Paul seemed to double down on Christ's words when he said:
For there is one God, and there is one mediator between God and men, the man Christ Jesus - 1 Timothy 2:5
The real question is, why would any Christian think that anyone of another faith actually is going to be welcomed into heaven by God when we have these two, very clear, verses in scripture.