A machine learning algorithm then uses that stuff to recommend content which is similar. If one engages with opinionated stuff, then they'll only get recommended stuff that conforms to their original opinion, forming an echo chamber.
The algorithm decides to show you more high-quality tweets and prettier photos.
If you consider that an echo chamber then all right, but I don't think it's a useful definition. Is going to a scifi-focused bookshop an echo chamber?
Looking at the list of things Twitter believes I'm interested in is quite enlightening about the limits of recommendation engines.