It had nothing to do with both of them. They could have shown any random monster at the end of the movie. Clover from the first movie was barely bigger than a building and now he is suddenly taller than the sky?
it's not the same Earth, yo
Cloverfield took place in 2008 in one dimension. This new film I didn't see what the year is, but it seems to be further in the future. Wouldn't it stand to reason that the alien/monster/whatever could be much larger in this future dimension?
I will agree they made it ridiculously huge, but we don't know how high those clouds were either :P
but it's also the same Earth because the scenes on Earth show you Clover's "first" attack.
That's the biggest problem with this movie. You can basically interpret it anyway you want.