When the girl in 10 Cloverfield Lane went upstairs to do a repair she came across a letter that appeared to be from a Japanese company. What did that have to do with the story.
It's an easter egg.
That company is part of the original Cloverfield movie. The company is the one that drills and releases/awakes the Cloverfield monster. The main character was also leaving to work/live in Japan.
The letter has no affect on the plot for 10 Cloverfield Lane. The two movies exist in a parallel dimension of each other, like any number of anthologies (Twilight Zone, Outer Limits, etc).