Yes, I can see how it may come across with a certain level of arrogance. Though I would say it's well intentioned based on the "mistakes" the author said he's made. It's been helpful to me for instance, to read about him getting over writing only "to document" and only when he "was told."
I agree. I couldn't understand what GP was talking about and I had to re-read the first three paragraphs to see what they meant when they said "snob-factor". On a second read I see where they may be coming from, but I still read it more as "I used to make mistakes, I now recognize those mistake and am a better writer because of it, here's the mistake I noticed, you can fix them too and become a better writer" than "I'm great. Wanna be as great as I am? Do as I do"
It seems that half the purpose of this is to convince the reader that the author is a great writer, speaking from a position of authority, followed by rather generic advice they generously take time from their busy day to offer: write more so you, too, can get better at writing.
Or perhaps it was all tongue-in-cheek, and I just didn't pick it up.