They're referring to loading the scripts right after the opening body tag (rather than at the end of the body), which historically would block content loading until the scripts all load.

Back then scripts literally were 1kb at most and not 15mb like today, so it really wasn’t much of a problem.

Back then it took ten minutes to load 1kb

It wasn’t that bad. I remember downloading fairly high res JPEGs (so 30-50kb) on a 36k modem back then, and that might have taken a minute.

Hyperbole is lost on 100% of people on the internet.