No, you were spectacularly wrong referencing state-of-the-art US MIRV warhead designs which were the results of decades of R&D, iteration, and a couple hundred billion dollars. You were suggesting something even more absurd than the Yugo car company being able to make a McLaren F-1. This was pointed out in said thread.
Lets also not forget that a MIRV is several nukes each of which can have the 400kt yield. All of the nukes are deployed so you do need to count them all collectively.
No. Different warheads, different targets. By that logic you could add up a couple million rounds of ammunition carried by an infantry division to a “weapon of mass destruction”.