A boolean can leave more than one: cutting a bar across its whole section leaves two.

 bar = solid.box (60, 10, 10);
 cut = translate (solid.box (2, 20, 20), [29, -5, -5]);
 numsolids (subtract (bar, cut))
 ⇒ 2

See also: solid.Shape.numfaces, solid.Shape.numedges

Source Code: solid.Shape