Yeah, I'm torn on this part of the advice. I think it cuts both ways in terms of getting the project done. Some new technologies are easier to pick up than others, so it's hard to paint that with broad strokes. The new tech is also sometimes the motivation for the project, and that cannot be discounted.
Though initial motivation by a new shiny toy that falls off is probably a big reason for the failure to launch idea in the first place.
There has to be a clear motivation for the project.
If the motivation is to use the new hotness than focus the project on that. Then setup the project in a way to properly gain familiarity with the new tech.
Whereas if motivation is a hot new idea and you want to see it to market, it is typically safer to use a tried and true stack and gain the joy of the wins of seeing the project advance.
My would recommend not tying a single project together with these two disparate goals, unless you plan on leaving one by the way side to see the other succeed.