"does this prove that they were more sinful ... Jerusalem? No, I say." Jesus uses this question to challenge the understanding of the people. Alternate translation: "you think that they were more sinful ... Jerusalem, but I say that they were not" or "I say that you should not think that they were more sinful ... Jerusalem" (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "I say" emphasizes "No." It may be helpful to state Jesus' point clearly. Alternate translation: "They certainly did not die because they were more sinful" or "You are wrong to think that their suffering proves that they were more sinful" (See: [[rc://en/ta/man/translate/figs-explicit]])