How the feck does anyone, apart from Pep, and others very close to him, no where he's going to end up at the end of the season? I personally think that tweet is BS.
Information leaks through various means. Most likely, as Bayern have been informed of his decision, they'd leak it to soften the blow when it's officially confirmed. Providing this is all correct, of course, but I don't see why you are sceptical of such news leaking, it's pretty much routine in football now.