Yup, so not only is this article preachy and boring (seriously, how many "I'm quitting $socialnetwork and you should too" posts do we need?), but it's also factually wrong.
Even if the from address was that of the user who sent the message, it's kind of hard to ignore the huge LinkedIn branding the message resides in. You'd have to be a fool to miss it, because I'm pretty sure even a blind person's screen reader would pick up on this.