They'd use GH to evaluate coding style and as a proxy for skill level.
It was a terrible proxy IMHO, because a lot of the projects or contributions they were looking at were years old. (People change and grow.)
Anyway, if there's a takeaway here it's this: Delete old repos that you wouldn't feel comfortable putting forward as examples of how you currently work. Or refactor the code to match what you'd currently do. Or don't maintain any public GH profile, frankly -- there are plenty of great engineers out there who have a family and no time to contribute OSS.