Let’s say there is a tulip lovers club, where they talk about tulips, their variations and how to grow them. Let’s say someone new joins the club, this new person starts saying that tulips are rubbish and that roses are better or something like that. This person becomes so insistent with these statements that they end up being kicked out of the club. Before leaving, the person calls the club an “Echo Chamber” about tulips.
Would this person be right?
Sure, from their perspective it’s an echo chamber for tulip lovers. In the end it’s a subjective pejorative, not necessarily a hard descriptive.
It also implies that actively ignoring opposing viewpoints is a negative thing.
There are plenty of negative and harmful things to exclude that don’t result in an echo chamber. Excluding nazis for example is not being a real echo chamber because there will never be anything new that could be said to keep it from being a hate based ideology.