Oh, he admitted to it, and it was popular (well, sorta; translations beyond OG Russian, Czech, & French were hard to get for a while) in socialist circles. Orwell accused Aldous Huxley of also copying bits from him, but Huxley denied it; I *kinda* don't believe him, BNW is very much more a capitalist dystopia than socialist.
All of them have bits from earlier utopian/dystopian books, but Zamyatin put it all together in one machine state.