I don't think that's true, thinking back to university, if I 'locked myself in a hotel room' and did nothing but study a given topic, I reckon you could get a decent grasp of more than one lecture course.

Of course not being able to ask someone any questions would be disadvantage (but is that even a 'rule' of this scenario? Surely at least the internet is allowed, i.e. a person to ask who's available to anyone), and it would have been a lot easier while at university than with X years' rust on the background maths etc. - but still, seven full days is a lot of time if you choose to completely dedicate it to some particular thing, we just generally don't do that, so it doesn't sound it.

Yup, prerequisites is all you need. I can go through any course of study in a week as long as I'd mastered it before.

Sometimes you have pretty much all the prerequisite knowledge but are still missing a crucial piece that would help you "piece it together" and make a significant advance.