Agreed - including many who should really know better. https://hpbn.com is an excellent resource to refresh or learn practical networking fundamentals.
It is... a domain for sale?
They probably meant this: https://hpbn.co/ but added the "m" by accident.
yes, thank you, whoops!
(too late to edit)
SORRY!
Typo in link to High Performance Browser Networking site -- aka HPBN -- correct link is https://hpbn.co