I guess this is just semantics, but look where this redirects to: http://en.wikipedia.org/wiki/Knock-off
"Counterfeit consumer goods, commonly called knock-offs, are counterfeit or imitation products offered for sale."
I've seen that too, but it's sloppy writing.
Knock-off: A copy, but doesn't use the name of the original.
Counterfeit: A copy, that uses the name of the original.
Fake: Doesn't work properly, or is copied only partly (for example using brass instead of gold), but claims to be original.
Imitation: Uses cheaper materials, but is upfront about it.
There are two attributes: Deception and Accuracy. Each combination of those two gets a name.
He said Knock-off, not counterfeit. A knock-off looks like the original but does not falsely advertise itself as actually being the original.