Oh sorry, I suppose I misunderstood something. It indeed is made from public repos.
But then again, I researched a bit and found the licenses to be a bit problematic, not that of Atom itself but the additional packages that are bundled in the binary. It includes some packages whose licenses are unknown and others such as Facebook's libraries(a lot of them) which have the non-free BSD+patents license. In totality the license of the binary doesn't seem to be a really good one.