Those who promote a flat earth have not benefitted from the experiences you've had. Since they have themselves seen nothing to convince them of the earth's roundness, they consider what you have seen and done to be impossible, and thus you and I must be liars, shills, or alternate usernames created by one of us round earthers. Military folks like you and me (Go Navy!) are often further accused of being active members of The Conspiracy, or dupes of it. In your case, you must have been an active part of The Conspiracy, since only by knowing the true shape of things could a navigation officer successfully return your aircraft to its base in that part of the world, where the globe shape diverges the most from the 'true' flat shape (whichever version of the falt earth your accuser holds true).
That's one theory. The other theory is: none of them believe it, they're having a laugh.
I am in agreement with both of your theories.
When I was in the US Navy I was an ET2 at the end of my enlistment, eligible for promotion to ET1. Most of my ET shipmates had at least graduated from High School and some like myself had attended or graduated from technical courses in a Junior College or engineering courses in University and had the advantage of studies in basic geography - knowing the earth was the shape of the globe in the class room and aware that the distance to the horizon was limited by the observer and was due to the curvature of the earth, etc.
When we studied Radar in ET School we just knew this already and that reinforced the fact that the Radar antenna had to be as high as possible for the greatest range of that Radar (SG-1b).
When we finally went to sea that certainly proved that the horizon is a distinct line were sea and sky meet , the distance limited by the height of the Radar or viisually for the lookout in the crow's nest. This dis-proved the flat earth fantasy of "The horizon is an indistinct blur which fades away at an infinite distance."
Same thing for the old flat earth fallacy of "Recovering to sight with a telescope a ship was has passed over the horizon."
So the bottom line is that we have had the opportunity to study, observe and put this to practical use. Unfortunately flat earthers seem to have not had these opportunities and simply believe the earth is flat because of their short-sided view that tne earth is flat on the ground on which they are standing.
Though I am really more in agreement with your "other theory." LOL.