You seem to equate a plea of ‘not guilty’ with ‘not confessing.’
That’s not what I said. I said that “not guilty” does not ncessarily mean “innocent”. One can plead “not guilty” if one is not innocent. If so, that can be understood as “not admitting guilt but contesting the charges”. But that is still not the same as “no contest”, which can be understood as “not admitting guilt but not contesting the charges”.
Functionally, the only thing that matters is whether one contests the charges. Which is why “no contest” (not confessing but not contesting) is functionally the same as “guilty” (admitting guilt and not contesting).