The idea comes after

Breaks filled with undemanding activity improved performance on already-worked problems by 41 percent — and only on those. The wandering mind keeps working on what the focused mind abandoned.

Sleep more than doubles the rate of insight on a problem you’ve engaged with.

So the break is not the absence of work. It is the second phase of it — engage deeply, disengage into a walk or a shower, and keep something nearby to catch what surfaces.