I feel like that commenter was a little harsh with that statement - I will say however that it has caught some flak as a source of truth. There are quite a few standards (principally, original jazz compositions by jazz musicians that have now become "standards", this probably isn't as much a problem for true "Great American Songbook" standards since those were always notated), that were transcribed incorrectly in original versions of real/fake books. To the point that many younger generation players are playing incorrect heads and/or changes to tunes since they learn it from the book rather than by ear. Not even that, but often they are just straight wrong, or dumbed down versions of the changes.
I mean yeah, I agree, I'm a longtime player. I appreciate DCSS's in-game discoverability. I find wikis useful for more in-depth explanation of game mechanics though. How combat rolls are calculated, etc. Ideally a wiki would provide that kind of deeper level of information, guide materials, etc.
Interestingly, DCSS's best source of info is the IRC bots/learndb.
I haven't played DCSS regularly since probably v0.24 or v0.25, so things may have changed - but if I recall correctly, it was not kept up to date very well, character guides are flat-out wrong, etc...