Doesn't matter much. Netflix has the data to detect VPN users among its customers, because it has a country from the payment provider.

If you connect to Netflix from a colo in the US and your payment provider says you're in Kazahkstan, Netflix has good reason to think that that IP address is a VPN exit point. When that happens two or three times with different customers and the same IP address, boom.

Maybe you've never visited /r/VPN on Reddit.