Yes, those are the sources from the January 20 version, the last version when the author used to care.
The current version (March 20) continues to have its sources private, and he only gives the sources to people that request it on places he likes, in ways he likes.
This isn't about the sources themselves, it's just some Stockfish that can use a Polyglot book, there's better Stockfish versions that provide the source, allow one to pile up to 4 different Polyglot books, and even allow people correct usage of the Cerebellum library, plus other optional additions. This is about THE COMMUNITY's indifference about Stockfish forks that are around that have their sources inaccessible or without a known way to get them (I don't know how the people that get the source do it, perhaps they're given a link to the source, and that link has no good reason to be kept secret.)
Apparently all this is about "credits", because if the exact same conduct happened but the author claimed he made the engine, most people would be pulling their hair out about it, but since the author gives proper "credit" to Stockfish's authors, then nobody gives a damn about the sources being shared.
I wouldn't do anything with the sources, it's just bothersome that I can't have them, when I ought to be able to have them. The difference between this and a fork like Raubfish, is that that is a private fork, nobody gets the sources, and at this point I'd rather have Stockfish Polyglot becoming like that, instead of this treatment where some get the source, and some don't.