> I only allowed to navigate the docs but not StackOverflow or google search, I thought this should be about showing my abilities to understand the problem, the given data and process it as much as I can and get a good result fastly.

To me this is a sign that they are overfitting to a specific type of candidate. And simply put, their interview process is not robust. If the underlying intent is to find a candidate who has deeper insight into their tools, as opposed to what can be gained via copy pasting blocks of code, you can probe that super easily without this contrived approach. Ask them about how their tools work, contrasting one option versus the other and so on.

IMO, you shouldn't overfit to this experience either. I mean, if we allow for the possibility that an Engineer can be incompetent/crappy, we should allow for the possibility that a Manager (prepared to bet that the hiring manager probably has the same ~ 4 years or so of experience managing) can also be below average.