Yeah in the past (e.g. Redmi 2) they released a Prime variant later with increased memory & storage size, but in this case it's not technically a Prime. There is only "Redmi Note 4" according to Xiaomi, and both 2GB and 3GB model have exact same software and hardware, only difference is the memory and storage size.
For all intents and purposes, the Redmi 2GB and 3GB models are the same device. The Pro or Prime label is not an official Xiaomi designation so it is literally false advertising.
They might release a Pro or Prime edition later on too, which actually has different hardware/firmware. Then it would be confusing wouldn't it?
No, that's not the official site. It says "Global Community". They don't make it clear that it is a fan/reseller site but it is.
The official sites are mi.com and miui.com (or mi.com/en/ and en.miui.com for English/Global portals), and there is only Redmi Note 4 - no Pro, no Prime, no "High Edition". Just the one model.
On mi.com/en/ (global/international) the Redmi Note 4 is not listed at all - which makes sense, because the Redmi Note 4 is only officially released in China. And when you go to Mainland China version of mi.com, you can see that there is only Redmi Note 4 - no other edition or model or variant whatsoever.
So, any additional designation is an incorrect re-seller or blogger label, wrongly applying older-model naming scheme when Xiaomi themselves have chosen not to.