While compiling the Qur'an, Muhammad was indiscriminate (even reckless) with the material he used as "Divine Inspiration". Many of his sources were pagan myths or legends, which were patently false. Although Muhammad did borrow from Jewish and Christian scripture, he could not even tell what was "cannon" and what was considered heretical. He treated it all the same! Whether it was a ridiculous Arab myth or a Christian legend, once Muhammad got a hold of it, it became fact! The very word of god himself...ALLAH!
Muhammad also didn't understand the difference between scripture and biblical commentary or opinions. This leads us to a very interesting verse in Surah Al-A'raf (7.1171), which states: When We RAISED THE MOUNT OVER THEM, as if it had been a canopy, and they thought it was going to fall on them (We said): “Hold firmly to what We have given you and bring (ever) to remembrance what is therein; perchance ye may fear Allah”.
Nowhere is this verse found in the Torah. But, Rabbi Avdimi bar Hama bar Hasa (long name!) did give his opinion on Exodus 19.17 which reads: Then Moses led the people out of the camp to meet with God, and they stood at the foot of the mountain. Rabbi Hasa's opinion is recorded in the Babylonian Talmud Shabbat 88a: This teaches that the Holy One, blessed be He, overturned the mountain upon them like an [inverted] cask, and said to them, “If you accept the Torah, it is well; if not, here will be your grave.”
This view was very troubling for many Jewish Scholars as it made Yahweh look Coercive and Cruel. Later Jewish scholars would interpret the Israelites at Mt. Sinai with a softer message. The famous Philosopher and Jewish Scholar, Maimonides, interpreted the mountain as being made of glass. Therefore the mountain serves as a window to view God. In this interpretation God is no longer terrorizing the Israelites but rather opening up a channel to have a dialogue. Thus a God that is kind and loving.
Other Rabbis had their own interpretations. Regardless, this is Rabbinical nitpicking on semantics. Rabbis often would have (sometimes absurd) extrapolations on various verses in the Torah. The Talmud isn't scripture and it's not meant to be read but rather discussed and debated. Muhammad didn't know this and mistook OPINION as the Literal Word of God.