Christians sacrificed animals as a way to compensate for humans. The ideas are similar in that God viewed human life differently but said to sacrifice animals because they were more of a material thing back then. Also, God tells Abraham to kill Isaac his son as a sacrifice unto God, but an angel intervened and substituted an animal. The idea was not so far-fetched to say that if no animal substitute was available that a human would be sacrificed.
What makes you so sure that he is a myth? Do you have proof? I see lightening, that could be his work. Sure natural means might exlain it, but why does it happen? Does it want to happen so it does? Thor must have inspired the lightening. What makes this so different from other beliefs.