Ken
I don't know how many of the spam on moodle.org are just advertisements or trying to improve their SEO and how many are malicious in the sense they'll compromise the reader in some way, whether clicking on the web or reacting to the mail in the mail client. I'm no security researcher.
About doubling the mail notifications, I didn't say the warning is malicious. Just that some people are sensitive to "too many" e-mail.
About the "practice for some time", I could be mistaken.
Yep, the "side bar" since https://moodle.org/mod/forum/discuss.php?d=451217#p1813549 has nothing to do with "Moodle Guide on Upgrading from 3.9 to 4.1".