Hi, Amar. The concepts talked about in the Cloud Practitioner course are very high level - meant to give an introductory understanding of how DNS works. In more advanced courses you will learn about features like weighted and geo-location, and latency based DNS routing. I can't say exactly how Netflix configures their DNS routing - but I am sure it is a complex combination of the features I just mentioned.
This is a great question - Netflix is very open about some of its engineering practices, but they like to keep their DNS settings pretty secretive because they serve different content to different countries, sometimes as a legal requirement, and people are always trying to get around this to access content they shouldn't. Speaking very broadly, a DNS server may use the IP address of the requester (you in this case) to determine where to route the request. There may also be geolocation settings and weighting as Tom mentioned, or they may cache content in certain edge locations that they know will be requested by certain DNS servers. The short answer is that we can't say for sure - but I love the curiosity. You will likely get some ideas on how they achieve this as you progress and learn more about AWS, but please continue asking thoughtful questions like this along the way!