I cannot even find the source... It's said it was "soon to be FLOSSed" 3y ago:

https://www.reddit.com/r/opensource/comments/e4en47/wtsocial...

3 years ago is about the exact time lemmy was first announced. An early alpha of a rust + react new reddit clone with some weird custom websockets is probably the opposite of how they would have wanted to start their codebase.