fish, the friendly interactive shell, is a commandline shell intended to be interactive and user-friendly.
fish is intentionally not fully POSIX compliant, it aims at addressing POSIX inconsistencies (as perceived by the creators) with a simplified or a different syntax. This means that even simple POSIX compliant scripts may require some significant adaptation or even full rewriting to run with fish.
Generally, people mix the two, so you have to use context. I think, however, your take is correct. I think the post is meant to give a bit of a rebellious vibe, so that may be why they chose this phrasing.