Lemmy is licensed under the AGPL, so they’re required to share modifications to the source code. I wouldn’t necessarily come out swinging at them, but you may want to inquire. lemmynsfw was also running a similar patch at one point, so it might be worth reaching out to them too.
Do you have a link to their backend or is it all custom? They seem to have done some inline video tweaking as well.
Edit: according to the donation post it’s all custom.
Lemmy is licensed under the AGPL, so they’re required to share modifications to the source code. I wouldn’t necessarily come out swinging at them, but you may want to inquire. lemmynsfw was also running a similar patch at one point, so it might be worth reaching out to them too.