If all the doctor did was confirm you're taking oxycodone, he really didnt do anything wrong. But if he was giving you stuff for it, accusing you of stealing or of the sort, then yeah he is in the wrong.
He should know the difference between the 2. How did he know your taking oxycodone? There is no way of telling the difference (oxycodone/OxyContin) by a drug test. Your chart would clearly say what specific medication.
It doesn't seem like something to get worked up about, you didn't share in your post that he made you feel uncomfortable or anything. It could have just been a misunderstanding.