Really glad I stumbled on this post. I really enjoyed 10 Cloverfield so I'm excited to hear that another movie is coming out. In the movie, it was interesting how it subtly related back to the original film (the satalite company the antagonist worked for...etc. It also had a lot of hidden messages. For instance, one of the big themes in the movie was domestic violence and the aliens at the end of the film represented the struggle that many victims face when they get out of an abusive relationship. Their troubles aren't over, they just begun.

The main character also talked about being haunted by the fact that in her past she remained silent when she witnessed an injustice (I can't remember the exact details) but then at the end of a movie she reaches a turning point and chooses not to remain silent going forward - she drives in the danger zone to help others rather than retreating to safety. This speaks a lot about how people remain silent in situations and retreat to safety rather than speaking up for those in need.

To answer the question:

how can a movie be a prequel to a sequel

I think the answer is that in the Cloverfield universe 10 Cloverfield ran parallel to the other movie in that both events were taking place at roughly the same time. So the new movie is a prequel to both movies actually.