The original statement "that the second condition of equilibrium means that
an object under the action of three or more forces may not be in equilibrium
unless the forces are concurrent" usually appears with the qualification
that the forces are non-parallel, such as the following positive form:
When three non-parallel forces acting on a body result in equilibrium,
the forces must be concurrent.
This form of the statement is the basis of several graphical forms of analysis
used, in particular, in Architecture.
The argument that parallel forces are automatically concurrent is not
a useful one.
Would the original poster would check the source and give the exact
quotation?
( The three-force condition cited above usually yields the value of
the direction of an unknown force.)