It never ceases to amaze me how stupid tourists go into a natural habitat and think that human rules apply in these habitats.
There are some good comments along with the article, one of them being:
"Quite what provoked the normally placid silverback into stamping his authority so forcefully is uncertain."
This statement shows the complete lack of understanding that animals are not here to entertain and amuse us without having thoughts and feelings of their own. These tourists were as far as the gorilla may have felt, invading his territory.
Are people that disconnected from reality that it would have made more sense if the gorilla pulled out his teapot and invited them all for a cuppa?