CS by Non-Parent?

I don't get this about someone ordered to pay CS, and later they find out
that it's not their child. How can that person still be responsible for CS
for a child that isn't his? Isn't that equivalent to throwing someone in
prison, later on finding out that they were innocent, and saying "someone
needs to serve time for that, might as well be you"? This doesn't mean the
father was messing around, it means the mother was messing around. How can
this get so completely turned around? All of a sudden we have guilty even
though proven innocent.

I just don't understand!

Roger N