What this fucking idiot doesn't TELL you is that that date isn't the date it was "published to GOOGLE" (there's no such thing) but the date Google THINKS that page was most recently updated / discovered - and it is VERY FREQUENTLY wrong, take it from me. And there's a MILLION things that website admins can do by accident to make Google think that.
I only made it through the first 10 seconds of his video before I saw what was coming...