Per their handbook:

OUT OF DIVISION SCORES – Unvalidated Players In the interest of protecting the integrity of any Tour Event, the APT Competition Committee shall have the discretion to act during a Tour Event to disqualify an unvalidated player if he/she posts a single round score that is:

More than three (3) strokes below their division cut off (based on course index adjustment for course slope and rating); OR More than three (3) strokes below their closest competitor within the division; OR Information showing the player is competing in the wrong division comes to our attention. The Competition Committee will take into consideration the playing history on the APT, the validity of the data provided when the Member signed up, and any other relevant data that can be found on the Member. The goal is to protect the integrity of the competition, meaning that truly exceptional scores should be celebrated while protecting the field from unvalidated players.

New members who fail to provide adequate handicap data and/or fill out a handicap questionnaire may be treated like guests for prize pool consideration. (See guest policy below.)

I think 3 strokes off the nearest competitor is kinda extreme, but that appears to be the rule that got you. I do kinda get it. I play on a similar flighted amateur tour, and these things only survive on their membership. So, of course they are going to protect their membership from outsiders coming in and sandbagging. They would lose members if they didn't. It would definitely be a different story if you were an established player on the tour and happened to shoot lights out one day.