Re: Weird..
Well it's not actually sending an automated SMS - merely setting up an SMS for the user to send.
I'd guess there is a mechanism to do this from within web pages for mobile phones - a kind of SMS equivalent to a mailto.
And a very quick search comes up with:
Making phone calls and sending SMS with HTML
That shows how to set up a link that has to be clicked (or tapped) - and seems quite a reasonable thing to want to [be able to] do.
So presumably what's happened in this case is that the bastard hard done by but generally very trustworthy advertiser has managed to find a way to make the phone think the link has been clicked, with a bit of Javascript or something.