You're right that container has been there for over a year.
The latest master plan does have that area basically split in half, but back at the end of 2018, they started doing the ground work with more of a 2/3-1/3 west-east split. At that time I think AMTRON's new Swift Center was going to be built on that plot but the separate Swift center seemed to get dropped (financing?) and "combined/replaced" the Common Facility Building further west. So early 2019 the proposed Nano factory was "expanding" and got located on that plot.
The container placement may have been to keep out of the way, if the factory was going to "fill" the western half of the two plots. But who knows with the limited info.
My conclusion about the 120k vs the 75k size is that they wanted to go 120k but had to scale back because the cost of the 120k factory exceeded the $82 million budget and/or Amtronics CC couldn't raise the entire $50 million to reach that budget goal.