For example, while Facebook, Apple, Google, and present-day Microsoft all are not strictly speaking monopolies (they have viable competitors) -- they each have various features that make switching difficult (but not impossible).
Which is a poor way to communicate a point when the widely considered definition of one of your words doesn't match the one you're articulating. It assumes everyone has read Peter Thiel's book (ps - everyone has not).
It's the same with the word "startup". For a majority of the world a startup is business that has just started, but for YC (well, pg specifically[0]), the definition is "A startup is a company designed to grow fast" and more specifically notes "Being newly founded does not in itself make a company a startup". The definitions are not only considered inconsistent but they're explicitly inconsistent.
Communication is important and this is one of those instances where I think many people might scoff at the notion that YC is building monopolies and that's "bad".
I'm just happy they're making this advice available.
EDIT: Here ya go https://www.youtube.com/watch?v=-oKjLVECMKA
The problem may be that that "tech startup" is too verbose and lame sounding.
All monopoly is contextual.
If you want to get pedantic about Thiel, he argues that the monopoly does not need to be the direct source of revenue - in fact, it's better if it isn't. Consider Google. What's their monopoly? Search engines, which they dominate with their superior product. How much do they charge to use that product? Nothing. Google makes all of its income indirectly, off of ads served via their monopoly (and other monopolies they hold, like email).
Facebook has a monopoly on Facebook, not posts, friends lists, and messaging.