The 5-minute thing as opposed to 5 hours, these are apples and oranges.
A group of musicians perfecting a recording already have the skills and knowledge which they are applying, and they will have mastered the piece they are playing. So they can go from evening to next morning. Same if you are learning a piece in a familiar genre in an habitual manner.
The "short session" thing has to do with acquiring skills; learning a new piece without picking up things which later you have to fix. For a truly new skill - say you've never played piano and you're trying to learn a scale on the piano - your entire brain will light up. Later there's a "designated area" which will be involved, and this is less fatiguing. You can also think you're focusing but actually you're partly scattered. A tight focus is quickly tiring but has strong results - that is, for learning.
I have also practised for several hours. But I'll switch what I'm focusing on. That includes working on one short passage, but focusing on different aspects of playing that passage. There may be mini-breaks where you stop, think about it or have some ideas, and then continue, in some kind of rhythm.
As I understand it, what MG is trying to counter is, for example, drilling the same thing for an hour. She cites some kind of traditional way which she seems to think is the norm, where one "does that". The professional band that recorded into the morning would not have been drilling something over and over to "learn" it.