"Howard had stated that 'they will attack all major population centers first, then send out ground troops to kill the survivors... Like us". The initial attack(s) that caused Howard to retreat to his bunker was [the Cloverfield monster]." --ImJonJordan
You know it. The Internet knows it. J.J. Abrams knows it. The 10 Cloverfield Lane title is loaded. Internet sleuths who spent months cracking the original's Augmented Reality Game, devising answers to the monster movie's whos, whats, wheres, whens, whys, and hows, would inevitably apply the same game logic to the new movie. Hints in the movie and the sequel's ARG invite curiosity, with passing references to Howard's job at Bold Futura, a space division of Tagruato, a mining company that may or may not have awoken the first Cloverfield monster. Intricate!
Abrams refers to 10 Cloverfield Lane as a blood relative of Cloverfield. Direct connections are limited to Easter eggs and the ARG. Think of it like a mirror universe. Or don't -- if anyone's inching close to a unifying Cloverfield theory, it's the guy above, who wonders if Howard, Michelle, and Emmett lived through the events of Cloverfield in the bunker. What if the attack on New York was just the beginning? What if Cloverfield monsters attacked all the major cities, and the "attack on the Southern seaboard" mentioned on the radio while Michelle's speeding down the highway is a similar event, the precursor to a full alien invasion? Sure, why not. Maybe the space-worm-ish creature that attacks Michelle in the grand finale is the fully evolved version of those subway-dwelling barnacles. Anything goes in the back alleys of Reddit -- a Twilight Zone for the Internet era.