Generally I would agree with you, but I think it should be taken with a grain of salt. "Hello World" is somewhat metaphorical concept, the ultimate goal isn't to show the label itself, but to show what is the amount of work required to produce some generic output without any business-logic involved. This means that it totally makes sense to use OpenGL or ncurses to show "Hello world" on the screen, even though they are obviously not necessary to do just that. It's just that they will be necessary for many other typical tasks we are considering.

So, although I wouldn't really chose tools author choses here, so the "not-really-a-joke joke" is still largely opinionated, I have to admit that assuming AJAX and some kind of MVC-ish framework (even if it's a one of your own) on both back-end and front-end is pretty much a must for a typical PHP web-application.

I don't think it's a joke, but I also don't think "tutorial" is the right word either. It seems more like an illustrative commentary on the state of the webdev industry.

Actually I'd prefer the program just consisted of plain text since that's perfectly valid PHP.