As the article says: this is not a general speed limit but an experimental speed limit for an apparently very crowded area where many kids cycle to school.
As someone whose 'normal biking speed' ist typically 30+ km/h on suitable bike lanes, I have no problems with speed limits at critical choke points.
Ah, this bit of crucial context seems to be missing from the entire rest of the discussion. Also makes what otherwise sounds like an uncharacteristically bike-hostile move actually seem fairly reasonable.
Tho tbf one still hopes that they come up with an infrastructure solution that makes it unnecessary in the long run.
I'm not sure whether the Guardian article mentioned this or another one I read: the road segment in question seems to be in the old town which makes it difficult to find an architectural solution.
In the Netherlands we do not bike for sport but for daily commutes and shopping. Most people on non e-bikes go at about 15km/h.