"Nolle Pros" means that the case is dropped. That's the good news. Nothing else really matters outside of the fact that the prosecutor has dropped the case. But, because you're asking--yes--sometimes prosecutors "add" stuff to the nolle pros document, explaining why they dropped the case.
Usually, "comp pti" refers to the fact that the reason the case is being dropped is because the defendant "completed pre trial intervention". PTI is a program that requires a defendant to do something (such as classes or community service), and as part of the pretrial intervention (PTI) the prosecutor is required to drop (nolle pros) the case once that stuff is completed.
This was not a probationary period nor was it court ordered supervision because you never changed your plea of not guilty and you were never sentenced. It was a diversion program that allowed you to resolve your criminal case outside of the criminal justice system. The case was not technically dismissed (only a judge can dismiss a case and in this case the charges were dropped by the state attorney) but a nolle prossequi has the same effect- either way the case is over and you were not found guilty.
Follow up answer is...it was not probation, but PTI carries on for a minimum of 6 months. PTI is a state-sponsored program usually requiring attendance in classes and/or community service hours. If all fees are paid, conditions met, and there were no new law violations for a 6-moth period, then the case is Nolle Prossed (dismissed) by the State Attorney. This program is only available to first time offenders and no plea is ever entered into by the defendant.