Is the Mandela Effect a parallel universe or proof of time travel?

I am not sure whether a theory similar to this one has been submitted, but I wanted to share the theory I believed the most. As many know, the Mandela effect speaks of a parallel universe, resulting in people having different memories of seemingly simple things. While watching a video on conspiracy theories, someone said that UFO's are theorized to be time machines (which leads one to ask: are the aliens people have seen just further evolved human?). Then, I thought about the Mandela Effect and how maybe there is no parallel universe. What if all this simple changes and alternate memories are a result on a human's presence in time where it should not be. Think about it: What if Nelson Mandela really was killed in prison but someone went back in time to save him? (disclaimer: I am in no way saying this is true, I am just offering up an alternate theory for you to think about).