Did you check the methodology? Relatively few Gen Zrs will own cars or have licences, possibly that was a survey of ALL gen ZRS irrespective of whether they know anything about cars at all.
I mean if someone has the confidence to actually drive, like on a road, why would they lack to confidence to use a petrol pump, but if you've never done it before, I can see why you might be worried about making a fool of yourself.
It must be a click bait survey with dodgy sampling to get stats like that.
It is a dodgy survey, but there were drivers involved. However, since reading, I have actually talked to someone (Gen-Z) who feels anxiety doing it, though they have been driving for a couple years.