Can't even have a proper discussion because the first commenter shut it down by attacking research methods. Let's just assume that this PhD didn't go around making a bunch of stuff up, huh? Have some faith and a bit of fun. And the commenters argument still doesn't disqualify all the original other's work.
I apologize for being uncivil, but I wish we could discuss this.
I should preface this with: My comments are based on skimming the piece. I did not read it entirely because I couldn't stand to. It is pretty safe to say that this is utter rubbish. There are tons of symbols that are used throughout the world and have separate origins, the swastika is a good example. The authors lack of understanding of what you can and cannot do with comparative stylistic artifact analysis is staggering. Images of mushrooms do not automatically mean there were mushroom cults or even if people ate mushrooms. Furthermore, the imagery he provides that is supposed to reflect mushrooms and fleur de lis is not at all compelling. This study falls somewhere between the muck on the History Channel and Von Danikin's Chariots of the Gods, not worth reading.
OP, fyi when you edited the post text, you inadvertently removed the link to the site in question.