Hacker Makes $360k ETH from a Flash Loan Single Transaction (trustnodes.com)

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.

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.

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