Waterfall in software development was different than a Gantt chart based "project that was managed" like the construction of a bridge (an example close to my house). They added new requirements to this bridge (like they wanted the surrounding grounds to be maintained nicely, so added irrigation and gardening etc). But no new requirements were added to the foundational "here's a bridge and it needs to cross this stream from this point to that point" (high level).

Waterfall in software was continuously changing those fundamental parts. You'd be fine tuning the irrigation and needed to destruct the whole bridge because some new requirements came up. That's where the anti-Gantt and "bad waterfall" comes from, the reality is the software world as a whole moves way quicker and requirements are way more malleable, subjective than building a bridge.