I'd say "sort of." Lemmy as a software is under a classic benevolent dictator situation. It's open source but as long as the lead devs remain two people we are kind of at their whim. Yeah someone could fork it but it's the same issue of you're now at the whim of that person keeping their fork up to date and what they want to do. Until they kind of allow more people having a say on the main repo it's up in the air what happens truly.
We've seen this same situation with Emby to Jellyfin. Where the open source project gets so good it goes close source, becomes a company and leaves everyone scrambling to get people to help work on the last bit of open source code. Meanwhile Emby just used their huge install base to upsell people. Jellyfin is still trying to get full parity with Emby despite Jellyfin having thousands of contributors and being open source. It's hard to keep up with well funded innovation compared to volunteer work.