How do I make regions like eu,us and india which lead to the same papermc server?

We can't tell you what your friend did, if he himself won't tell you.

It nominally sounds like he's implemented something like CloudFlare's regional caching… but I've never heard of that in Minecraft.

For HTTP, there's plenty of opportunity for a regional proxy to improve performance, due to the static, cacheable content system. Even dynamic web content doesn't suffer terribly from asynchronous updating. (e.g.: If you have to wait 10 seconds for your regional proxy to update to see a new forum post, you'll barely even notice. But 10 seconds of lag in Minecraft would just be untenable.) There's a real difference between a website, and a real-time RPG with synchronous play and a physical, fast-paced combat system.

Here's a thread where even one of the biggest Minecraft servers, with a heavy international community, is apparently not even considering it (in fact, the idea is so far "out there" that the only responder gets the idea confused with non-proxying transfer packets.)

tl;dr: My best guess is that either your friend is lying for attention (e.g. the in, eu, etc. subdomains all just have the same underlying A/AAAA records), or he's implemented ("in Node") some kind of regional proxy which will only slightly increase latency for any international players. Regional proxies have a use-case, and Minecraft isn't it, unless he's done some heavy server-side modding as well.