Tawatur is not a religious term. It indicates a historical fact transmitted from generation to generation to the present generation. For example, the person and achievements of Alaxander the Great, or the person and contribution of Plato have been transmitted to us through Tawatur. People come to know of them as a historical fact. The documented pieces of evidence are secondary and supportive of the claim that these persons really existed.
Tawatur is about the historical facts and can be traced back in history; the exact or approximate date of these events is known.
Mythology, on the other hand, does not have a historical connection or chain to confirm its date in the past. Therefore, historians do not record mythology in their annals of history. Ram and Karishna come from Hindu mythology, not from Hindu history.
Events like the crucifixion of Jesus are transmitted through history as a fact. The people reported it the way it was shown to them. The Quran tells a hidden fact that Jesus was not crucified; another person was crucified in his place. Since it was a hidden fact, the onlookers did not report it.