I don't know how much in the way of smarts he really employed in this - a fully fueled 767 carries upwards of 20,000 gallons of Jet fuel - more than enough I suppose he roughly calculated to do damage sooner or later ...
I honestly don't think that he foresaw the amount of complete and total devastating collateral damage that would occur to other buildings in the area though.
He most likely knew only one thing - the tower fires would *most likely* never be extinguished by the sprinklers (even *if* they were working) and at some point the structure would *have* to fail (again, designs must accomodate *some* fire endurance, with engneering training he would know this) - and knowing this limit, simply exceed it and succeed in bringing down a tower (or two) ...