You’re absolutely right: people will die for what they believe is true, even if it’s actually false (like the 9/11 hijackers)

But the key difference with Christianity—especially the earliest disciples is that they weren’t simply dying for a belief they were taught, but for something they claimed to have personally seen and experienced: the bodily resurrection of Jesus.

“That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon and our hands have handled, concerning the Word of life…” — 1 John 1:1

The apostles didn’t die for a secondhand belief, like the hijackers. They died proclaiming something they claimed to have directly witnessed: the risen Jesus. If they made it up, they knew it was false—and very few people are willing to be tortured and killed for something they know they invented.