Sync for Reddit was around for a long time, about 10 years. It came out before the official Reddit app, which on release had a design that was heavily influenced by Sync at the time, and still to this day has some design elements it took from Sync.

Sync for Lemmy may be a "new" app, but it inherited almost everything from Sync for Reddit. If anything, others are copying Sync, not the other way around. What you see in sync for Lemmy is the result of about 10 years of development and refinement from the reddit days being ported over to work with Lemmy.