The study of luck is called ludometrics (there are a few interesting papers related to sports on Arxiv). It is very tricky and there are several competing notions of luck...I am not convinced that the method in the article is particularly useful, particularly as it involves human decision-making where you see power laws all the time...which doesn't necessarily indicate luck. Maybe you could argue that the scale of the success is outsized but this is largely a function of the way people consume, not luck...I don't know, it is tricky (and I have spent a lot of time looking at this problem in sports).
Good question. At least one for me is that I'm only interested in variables that are usefully measurable up front. So if somebody starts a business before the factors that make it huge are reasonably discernible by people at the time, I'd call that luck.
I also think things that are outside of the control of the actors are reasonably called luck. E.g., I'm in software in good part because my dad happened to get into software in the 1960s. He only got into it because his dad was well placed at a company that wanted to automate a lot of then-manual appraisal calculations, and they pulled him in to figure it all out. A couple years earlier and he'd have been too young. A couple years later and he would have been gone from his home town.
