Not sure. There was some controversy with some of the devs making alt front ends and admins complaining about the slowness. I’ve seen mention of one of the two devs learning Rust just to participate. So it is not entirely a walled garden. The front end devs wanted to make an alt from scratch but in something like JavaScript although I don’t recall the details exactly. There were a lot of red flags related to privacy and understanding the community at large in the posts I saw from them. When asked why they weren’t adding pull requests with Rust in order to address their complaints I got no reply.
All that said, I’m no dev. I can read in to around half the code I come across if I really try, and can successfully modify maybe half of that if I spend a few days on it, but I suck at clever code and the DRY cult types. I haven’t tried to look into Lemmy in any depth beyond figuring out the basics.