I have seen guns with rifling nearly worn away from extensive "use". But not from shooting, from cleaning, using the wrong stuff.
On a guess, I would say really badly leaded is much more likely than anything else, but a factory goof is possible.
As to the legal issue, mere possession is a crime. Generally, if there is nothing else suggesting you are responsible for removing the rifling, prosecution is rare. But it is legally possible. Its kind of in the class of a malfunctioning semi auto. Something that is a technical crime, but circumstances play a big part in the decision to prosecute, or not.
Your gun goes full auto (maybe only doubles, or even runs away), you send it to get fixed right away. If the BATF hears of it, they note your response, and usually don't bother with prosecution. They could, but they usually don't.
However, if you keep the gun, because you now have a cool machine gun, and they find out, your not even trying to get it fixed means you are willfully flaunting the law, and they do like to punish people who do that.
Am eagerly waiting to hear what Colt says / does with your Python.