If your book stated that using a small amount of detergent would remove heavy soiling better than using a larger amount for a single wash, then I say it's bunk.
If your book stated that using too much detergent on a regular basis could result in a dirtier wardrobe, then there is a good explanation for that.
Let me use a more common but analogous process to explain: carpet cleaning. Though detergents generally work best in aqueous solution, residual, dried-up detergent still tends to bind to organics (or various types of undesirable "dirt") pretty well. So when one has a difficult to remove stain, they clean it repeatedly with highly concentrated detergent solutions that do not get thoroughly rinsed out of the carpet. Then, even if the stain is removed, that area quickly becomes soiled again due to the residual detergent sticking to more dirt than the rest of the detergent-free carpet.
Tying the carpet-cleaning analogy to laundering clothing is then pretty straight-forward. If one always uses more detergent than can be reasonably removed during the rinse cycle, then their clothing will tend to soil again more easily than if they had used an amount that could be largely removed during the rinse cycle. Thus, regularly laundering with too much detergent could result in a dirtier wardrobe than using a smaller amount of detergent.