It’s basically like a Hubzilla channel which, in turn, is somewhat like a Friendica account. Which, again, is very vagely like a Mastodon account.

To my best knowledge, you can’t follow individual accounts outside the Threadiverse on Lemmy.

In addition, (streams) has recently switched to decentralised IDs as per FEP-ef61. This could be the reason why Lemmy can’t find my (streams) channels, but it can find my Hubzilla channels: It doesn’t understand DIDs.