There's one major problem with his theory: Nuclear weapons are not something you manufacture and it just sits there, ready to use, for decades. You must maintain it. We have a freeper here, Squantos, who did just that for a living.
If you don't maintain it, it may or may not function. It COULD be used as a source for a dirty bomb, and that's bad enough, but as far as a functional nuclear weapon? Well, Squantos -- if he cares to chime in -- could tell us the likelihood (or lack thereof) of a four-decade-old Uke Nuke, unmaintained, to actual go bang.
Now, an Iranian nuke is a possibility, and our gov't just let it slip (by inference) that they likely have something, but I would speculate that anything Iran controls is unwieldy and has a smaller chance of being functional than one of the major power's weapons.
I had the same thought. Maintenance is key with nuclear warheads and ‘vertically deployed’ devices. That doesn’t disprove Mr. Ferguson’s theory, but it does warrant consideration.