You can definitely measure it. I've seen many times where people were struggling with problems for months with tons of operational incidents, before someone experienced came in and solved it for good in a couple of days.
So even if we believe in the hypothetical general purpose 10x programmer, a 120x one seems a little implausible, right? I think it must be a domain expert or something was really dysfunctional about the original team.
In practice one very good guy can achieve as much as a whole badly managed organization.
It's not necessarily that he's that much better technically, but he's got the right drive, focus, and business acumen, and isn't bound by methodology or legacy.
The real problem with software development is that a lot of developers are too removed from the business to deliver something practical with value in the right places.
Or it could just be somebody that happened to have a crucial bit of domain knowledge.
Or the original composition of the team could have included some negative-contributors.