That's a post about invalid things that are not IPv6 addresses.

In IPv6 addresses, :: is all zeroes and there's no ambiguity.

I am not clear what your point is. The parent's point stands. A double colon only represents zeros (that were compressed and are not displayed).

Your link does not show different addresses from a valid compression, it shows different addresses from an invalid compression. The link examples what we don't do.

Conversely, if we compress the expanded addresses in your link, we will get 2 different compressed addresses.