Exactly. The hard-drive loss is a taxable loss event for which he can only deduct $3,000. But mining the coins gave him an income (the value of the coins when mined) and a capital gain (the value of the coins when lost minus the value when mined).
Except for the obvious fact that the value of lost coins (or any other lost or destroyed property) is
zero unless they are insured (in which case the capital gain is the
insurance payout minus the value when they were mined), meaning losing the uninsured coins is a capital
loss event, which is exactly what the article says.
He would deduct the $3,000 from the earnings and capital gain (minus mining expense) and pay taxes on the difference. This is why the author says it's a "double whammy": i.e., not only did he not get is $7,000,000. He also lost his ability to pay the taxes he owes on that $7,000,000.
He does not "owe millions of dollars in taxes", nor does he owe taxes on the $7,000,000, and the article never says either of these things.