I think you're getting caught up on the wrong thing here. The issue isn't that monoliths can scale. The issue is the inherent flaw in their logic within the confines of the post.
Netflix also didn't appear into existence with an army of engineers. It also scaled from a few engineers to what it is today. Which means you can scale using both depending on your setup. That cannot be the reason why you pick one arch over another. The reason has to do with your own setup, your company, and the application's specific context, all of which the author is missing.
Broadly, it feels like decision making without context/understand the why behind the decisions.
The specific comment has nothing to do with how Github or Stack Overflow scaled etc.
