Open source to some extend, but their whole thing about these emojis is that they are 3d and animated. But the repo only contains png renders if the 3d models. So you arent able to modify or animate the 3d models directly.
Imo they released enough to call it “open source” and get good PR from it without actually giving the raw source files to the community (their competitors). I was not pleased with this when they announced it 2 years ago. Its still the same.