I'm in Colorado so cannot say for certain. My guess is that because you forgot about the ticket and did not appear in court, the court entered a default judgment against you. This is typically done in minor traffic violations when the person does not appear. What that means is that the judge entered a guilty verdict against you because you did not appear when you were supposed to. However, in Colorado, this usually means there is a hold put against your license until the fines and court costs are paid. You said you were stopped recently and no problems which could mean the officer didn't have access to it.
How did you come across the information that showed it was a guilty plea? Is it on your DMVR or did you contact the court in Tulsa County? I would do both of those things to make sure there isn't anything still open or outstanding on that ticket if you've never paid any money on it.