You forgot the second part, which really justifies his fears. The whole quote:
"I've had a pest man around to sort the problem and he said there were still thousands of wasps around. He warned me not to go near there because they might smell the stings on me."
And apparently, the stings and the smell are like markers for other wasps to attack (according to an expert in the article).
Even without being stung prior it'd still be nope for me. All it takes is one out of the bunch to get offended and release some pheromones and then they're all pissed off at the snap of a finger
As a former "pest man" I can't imagine going into a situation that intense. They sent one guy and he's like don't go back out there. What the fuck? Need to send a team in suits to deal with this. In my post exterminator life I don't kill anything except mosquitos and wasps. But I do so with extreme prejudice.