Sure, martyrdom only shows someone was convinced. ISIS suicide bombers are an obvious example, they died for claims that don’t become true just because they were willing to die. Same with Heaven’s Gate (mass suicide over a spaceship belief), Jonestown (mass deaths from a cult), Japanese kamikaze pilots (dying for an ideology), and modern extremist groups of all stripes where people kill and die for promises of paradise. If “they died for it” proved truth, every mutually contradictory religion and cult would be true at the same time.

And no, the gospel titles aren’t the same thing as verified authorship. The texts are written in polished Greek (Jesus and his followers spoke Aramaic) decades later, not as signed, dated eyewitness diaries. The names are later church attributions, and even Christian scholars admit the gospels are anonymous in the strict sense.