You're completely missing the point.
There was absolutely no need for B Johnson to open his gob and say anything.
The Foreign Secretary may be very limited in what he can do to help an Iranian-British dual national in Iran. This is a well-understood issue with dual nationals of most countries.
But only someone who either:
a) was trying to make things worse, or
b) was too dim to grasp or simply didn't care that what he was saying would make things worse,
would publicly open his trap and spout the things Johnson did in the role of Foreign Secretary.
Neither of those two alternatives is attractive. And neither suggests Johnson's a fit person to hold high office. If it's (b), this is far from the only time he has behaved like this.