That is simply not true. It is just barely possible that some people at the time did not know the difference between the teaching about purgatory and the teaching about hell. But Tetzel on a bad day never said that anyone could purchase release from hell. It beggars belief to read that anyone who's looked into this would say that the Pope had put his seal to such a thing.
Do you have some kind of evidence? I've seen what purports to be an indulgence from the time, but I don't recall seeing anything about release from hell.
Even Catholics admit that Tetzel's writings penned the tune:
What beggars the belief is that a lone monk could have instituted such a policy. Please remember that Luther's 95 Theses was addressed the issue of indulgences and provided an opportunity for the Church to renounce the practice. They never did until about 100 years later.
Tetzel, on the other hand, who was this poor misguided monk received full burial honors by the Church.