When a job offer is rescinded I think it would be fair to expect them to tell you why? They obviously feel they have a good enough reason. Now if 6-7 others in your group got the same notice, then it's a bit murky. I can't imagine that happening unless there was some major observation made (cooperating during testing as an example).
Remember there are cameras everywhere these days.

For anyone who is interviewing, the key point is to be yourself and be honest about your past. Sometimes, we fret about things that seem like a huge burden, only to find out when we get older that they were not as important at all.

Not everyone has a perfect record. In your career, there will be ups and downs. Someday, you may have a bad day in the simulator, on the line or an examiner who gives you a pink slip. It happens. Disclose it and let the airline make the decision on hiring you. It is much better not to get hired than to be fat dumb and happy in class or on the line and get yanked.