Does counterfeit money prove that actual money does NOT exist? Of coarse not In fact, counterfeit money has no purpose without ACTUAL MONEY in which it copies...
Jesus said that He alone was the real deal - the way, the truth, and the life Therefore, Jesus said all other systems are false...
Does this seem like a reasonably possible explanation to you?
If the person asks where's the proof for God/Jesus/Christianity, go here.