Doesn't really matter if they open sourced, since many reddit alternative over the years have been open source: Voat, Ruqqus, Raddle, doesn't really make.a difference since they all failed one way or another. They either never hit that critical self sustaining mass of users, or they attracted the exact wrong type of users who drove out any reasonable users there.
Federation seems to be the only way to create that critical mass of users, and Lemmy is the only alternative that really succeeded (kbin is kinda...hanging on for dear life for various reasons but is alive only due to federation) precisely because it is not a website, but a platform inside of a greater ecosystem.
All Discuit really have is a pretty UI, as it is nowhere even near feature parity with a current defederated Lemmy instance, and Lemmy also has like a dozen different desktop and mobile UIs already.