At first glance it occurs to fantastic to be true, but on the other hand I've seen and experienced an impressive level of stupidity among tourists before.
Like trying to handfeed a bear in the zoo with Maryland cookies...
For all I know they could have been walking in a too close proximity to the border and then aprehended by a Iranian border patrol simply because they had strayed into one of the numerous minefields left there.
Or they could have attempted some kind of smuggeling or other tricky buisness.
Most interesting fact is that the Iranian authorities didn't bother to keep them there, indicating either covert diplomatic activity, or simply that they were certifiable lunatics.