The content is being served by many peers on the network. You find the peers through a gateway - ipfs.io is one such gateway but any peer can also act as a gateway.
When you visit the page via ipfs.io you are viewing it via the ipfs.io gateway. The ipfs.io gateway has complete power to censor content, serve malicious content, etc.
You lose most of the benefits of IPFS if you browse via a gateway controlled by somebody else.
You don't find peers through a gateway. A gateway is literally just an IPFS<->HTTP gateway. The gateway does all the IPFS stuff and just serves content to you over normal HTTP.
The content is being served by many peers on the network. You find the peers through a gateway - ipfs.io is one such gateway but any peer can also act as a gateway.