Judging by their stats they must have had data on 150,000-200,000 e bike trips overall. So if you treat each trip as an relevant event for determining the crash rate - then I think it’s a decent enough sample size of eBike trips. It’s just they had heck of a lot more of eScooter data.

The main biassed I’d think are around the rental companies they got data from, and the customer populations. And that they have basically only 7 cities.

but the findings were remarkably consistent over 3 measures of exposure and within each city except Dusseldorf (not enough ebikers to have any crashes).

A couple of the p-values were over 5% or 10% , so some were weaker when narrowing down to an city or just one of the exposure measures - but still a fairly consistent pattern.

Than e-bikes? Are you mixing up kick-scooter-style e-scooters that people use while standing on them with sit-down vespa-style scooters?

They are talking about the stand-up version, which are smaller, slower and lighter than e-bikes.