Bit surprised this works. Latency variability is huge and sometimes quite disconnected from geo location. I recall talking to someone in NL and realised I've got better latency to NL content from the UK than he did. Presumably better peering etc.
Wouldn't you just be closer to the closest PoP and requesting mostly cached content? With how connected amsterdam is they couldn't be around there. Also depending on when it was up until like 7-8 years ago even in major city centers there was no fiber in most places in NL. Now it's mostly covered.
Could just be local loop latency, in VDSL or DOCSIS you can get 5-15ms of latency just in your first 1KM. London (e.g Telehouse) > Amsterdam is only about 7ms.