Hacker Makes $360k ETH from a Flash Loan Single Transaction

Flashloans are a kind of loan where you can borrow a potentially large quantity of a digital asset with no collateral for a small fee — as long as the asset is returned by the end of the atomic transaction.

It looks like somebody very cleverly used a large flashloan to, essentially, create an arbitrage opportunity by moving the price on a relatively illiquid asset.

From tfa it sounds like they’re using the traditional definition of hacker and not shorthand for someone who uses computers to steal from people.

I don't understand why this is considered a hack.