Polygon is a protocol described as an 'Internet of blockchains' that is compatible with Ethereum and connects with other Ethereum-compatible blockchains.
They suffered an attack on its blockchain that affected other blockchains and the coins affected were sent to the hacker's address.
From my understanding:
Polygon (formerly MATIC) is a token related to (built off?) ethereum.
Poly Network was a bridge layer that spanned polygon and ethereum.
Polygon and Poly Network are distinct entities as far as I can tell, but they are all overlapping and using each other, so I don't fully understand the distinction.