It's a direct quote from one of the scientists:

'"I was absolutely stunned when I first saw the results," Prof Chris Griffiths, a senior author on the study, at Queen Mary University of London, told the BBC."'

Scientists are only allowed to be stunned when results exceed 5 sigma of deviation

To be fair, BBC is aimed at the normies, not the scientifically literate. (No hate on BBC!) Stunned probably gets more clicks than surprised.

Smokers don't magically undo the damage they did to their lungs after they stop smoking. Stunned might be hyperbole, but it is at least a little bit surprising.

Sounds like an announcement of the latest AI news from Wes Roth. I'm surprised the Professor wasn't "shocked"

I'd like to imagine the stunned scientist is a scientist from another field, they show some medical findings to a guy who looks at snail butts all day and he's the one "stunned" by the findings

I'm obviously supportive of less pollution etc etc but looking at the actual graph results I wouldn't describe them as 'stunning', the needle barely moved. But of course, they have to have something to make headlines after spending so many million on the study and who knows how many billion on ulez. I'm not one of these anti ulez people I think it's good. But you can imagine the pressure to spin tepid results into headlines.