Why dont you find the author and email them. I read your questions on the link. The reason there is no wiki on it is because some random person that is in no legal way using the Godzilla trademaek is writing it. If you go to fanfiction.net and look up godzilla or superheroes or whatever half the stories are gay romance novels that involve crossovers with random characters. Godzilla having sex with people. Imagine if they had to make every persons personal takes and stories as canon. It would be retarded.
Guy who uploaded it literally calls it a fanzine. If it was official they'd be any sort of proof that calls it official. Official canon doesn't try to hide itself.
A talented artist drew it up and made his own story for it without the authorization of official sources. That's it.
This also doesn't involve comics and could have been asked in the questions thread even if.
Japan isn't US. Not everyone gets sued. Not to mention a lot of these people are actual manga artists with real jobs (for example look how talented he is, unlikely he doesn't have a job drawing). Hell he could have been working on actual Godzilla mangas for all I know and it still wouldn't make it canon. I suspect you'll try and turn this around to say his word is law or something fully accepting that he worked on official Godzilla mangas...
But we'll make it real easy to see if it's canon. Is it licensed by Toho? No? It's not canon then.