What is confusing about that? That's like complaining that you can write an IPv4 address as 001.002.003.004 or 1.2.3.4. Even the :: isn't much different from being able to write 127.0.0.1 as 127.1 (except it now becomes explicit that you've elided the zeroes).
While it's possible to write an ipv4 address in a bunch of different ways (it's just a number, right?) nobody does it because ipv4 standard notation is easy to remember. Ipv6 is not, and none of these attempts to simplify it really work because they change the "format". I understand it and you understand it, but the point here is that it's unfriendly to anyone who isn't familiar with it.
