That’s the implication of a quotation erroneously attributed to Einstein (as Bill Vallicella notes):
If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?
Clever, regardless of who said it, but too clever by half. A cluttered desk isn’t necessarily a sign of a cluttered mind; a person with an orderly mind may have a cluttered desk and still be able to quickly retrieve from the clutter whatever item he needs. An empty desk is a sign of a person who likes order (neatness, symmetry), which usually reflects an orderly mind.
A cluttered desk may be a sign of an orderly mind; an empty desk is almost surely a sign of an orderly mind.