That's not waterfall as used in the conventional sense. A key element of waterfall was/is: "Thus the waterfall model maintains that one should move to a phase only when its preceding phase is reviewed and verified."[1]
>The details vary, to be sure, but the fundamentals remain the same.
I disagree. Agile is distincly different at a fundamental level from waterfall. If you walk into a modern shop doing mostly agile with continuous delivery, you'll find that there is almost no process at all that maps directly to waterfall. Literally, not a single one: not design, not coding, not testing, not building, not deploying. They're all fundamentally very different. Coding is probably the one that comes closest and if the site uses TDD or pair programming, it will be clear how drastically different even that is. [1] https://en.wikipedia.org/wiki/Waterfall_model