That's strange. I did not have to. I wonder if it was based on your user agent, or some anti-crawler detection?

I have noticed this with a lot of websites recently, things like Twitter and Instagram only sometimes ask me to log in to view things. Reddit as well, will be happy to show me some article, then later that same day it'll ask me to log in.

You are right. I logged out, and then proceeded to view the gist without logging in. Maybe they left some tracking cookie after log out (like device id), or they invalidated my previous session and triggered login on that invalidated session.