The fact that the community has been able to use the published paper to replicate all of AlphaZero's results in both chess, go (and a number of other similar combinatorial games) and get similar performance should lay your concerns to rest.
1. Deep mind kept a lot of information about their methods undisclosed.
2. Despite all the claims of generality, the algorithm requires insane amounts of fiddling to train. Just read their blog.
3. The hype around AlphaZero crushing every other algorithm in chess is overblown. It's competitive, but not clearly superior.
Still, Kudos to people running Lela project for doing what DeepMind should have done - describing how things really work and testing in real-life conditions.