Earlier quoted context omitted.
That might be how some client(s) work, but I don't think that is how IPFS works. If you access a piece of content over ipfs.io for example, I would think you just make https requests like to every other website.
Because its using a gateway. I think if you are accessing it natively through IPFS, it will default to adding you as a peer.
But it is a protocol.
I would not expect that the protocol specifies that a complient client shares what it downloaded. That sounds more like a choice the client developers make on their own.
But I'm happy to be corrected if someone has a link to the protocol definition and it says different.