Definitely not. That's been a thing for at least as long as mod_rewrite has existed (and I'm sure there's prior art). It was common long before GitHub.
It happened, but not as often as you'd think. In 2017 I was arguing with someone that the back button should work and URLs should be obvious in a fairly large project and they said "people are used to the back button not working - like a bank website".
1. not use query params for key entities in the URL
2. to stick user identifiers at the root path! totally unheard of to occupy such an important path at that point!
Taken together, this was entirely novel. Next to nobody did this. Twitter was the one other notable example, and that's literally all I can think of.
The URL bar was so different back then. It wasn't search by default. The average tech savviness of internet users was higher. People cared about URLs despite the fact most websites had garbage cgi-bin query string slop. Lots of folks had personal domain names. People typed URLs and shared them a lot - so this was a big deal, because they were memorable, unlike the other slop URLs at the time.
To give more character - HN's urls would have been considered exceptionally nice back then. The average URL was way worse and was littered with hundreds of query parameters.
A great deal of websites put your session token in the query params. PHP had first class ways of spending "sessions" to all urls. Essentially a cookie. It was disgusting.
GitHub revolutionized urls as a product. Even today, not many companies followed suit.
Reddit did it, linked in, most social media really, this is all just a throwback to /~user/ paths from apache and other early webservers. I think slashdot used the same convention.
3rd level would be yourname.site.com, like LiveJournal and Blogspot had a long time ago.
4th level would be site.com/yourname, like Myspace had a long time ago, and Facebook had after that, and Github had after that.
Once you sink all the way down to the obscure depths of 4th level, there's not much difference between site.com/yourname and site.com/whatever/yourname
