Which is rather ironic.
Iceland actually DID "stop a volcano"... (well sort of, or at least they tried....)
There was a lava flow that threatened to cut off a vital harbor, so in desperation, the Icelanders went out in ships with pumps and fire-hoses/water jets etc. and tried to harden/divert the flow to prevent it from completely closing off the harbor.
There's some debate that the thermal mass of the flow was just too great for any amount of pumping to slow or stop it, but the flow did stop in time, and actually made the harbor better and more protected.
So it's kind of funny for you to mention this. Because AFAIK, the Icelanders are the only people who have ever tried to "Do something about it."
Of course the basic premise of your acquaintance's stupidity is not in question here.
What I want to know is, if this is the "Worst ash-eruption in 100 years from Iceland to blanket Europe, what did all the commercial airlines do about it back then?"