We then proceeded to ignore this entirely and for the rest of the course acted implicitly as if we were using waterfall. Including in subtle ways, such as being given homework assignments due next week with no chance for iteration. An "assignment" in which there is no room for iteration bears absolutely no relationship to the practice of software engineering of any kind.
In hindsight, thinking back to my software engineering course, I'm not sure there's a single thing in it I agree with ten years later, and it's not like any of the things I've learned in those ten years are brand-new knowledge, it was all equally obvious in 1999.
What they didn't say is that describes virtually every project.
Meanwhile, web applications (that aren't Google-search scale projects) don't require any software "engineering"—they're simply designed and then crafted, more like a clay pot than a bridge. They're iterated like a play is rewritten slightly after each performance, based on audience approval and obvious errors, not based on any accepted theorem or body of knowledge that says that the given practice is wrong.
A corollary of that statement is that Software Engineering has no use for most of us here at HN :)