Lemmy is Free Open Source Software allowing anyone to host a content aggregator website. Lemmy instances can federate with each other to make it look like one big website to users. It was created from the ground up to avoid corporate influence.
A group of people working together towards a common goal while doing their best to avoid corporate influence is probably going to be mostly liberal minded.
I don’t see much of an echochamber though, although that’s probably because I block a lot of it. I prefer a post have a well thought out argument rather than “lol conservatives dumb”. If someone had a well thought out reason for being against a liberal policy I’d give it an upvote. It’s just that these rarely exist. It’s mostly just reactionary comments.