I assume the grandparent is making a (quite funny) joke about destroying the global economy by virtue of the delivery of the asteroid destroying the Earth.
Probably similar to how the Spanish conquistador's precious metals haul from the New World decimated the economy of Spain: massive supply/demand imbalance.
Except that we are not 400 years ago when money was gold.
A better analogy would be if they towed back an asteroid full of $100 bills.
"Now if they find an asteroid that is made out of Bitcoin, that will be economically significant."
-Matt Levine