sorry to hear about your experience. you are one of the most enthusiastic weares and i feel your pain with what happen....
similiar to what topcat said......i have always inspected peoples hair even before mine was thinning, i was always concerned with hairloss because my father was bald.
i would always be looking at my friends hair for signs of balding (i'm talking bout from the age of 15 on!!) as well as strangers.
this become even greater when my hair did begin to thin.
i'd look at others to see if it was happening to them too and i still do. because i'm always looking its easy to notice something, something that might not be so evident to another who is not so hair obsessed,
thats what i think happened here. he is probably always checking people to see if they are losing it too. not just checking but real scrutinizing. if anything is just a little off people like that will probably notice.

also with you looking up like that he was probably looking at your hairline from underneath as opposed to straight ahead. what i have noticed is when i tilt my head back or a sideways look at the hairline in certain lighting i can see a white line unless the attachment is perfect. being i'm obsessive i look at my hairline from all angles and in all lighting conditions...from straight on ya cant see a thing though... this is also true with indirect light. in a cars review mirror for example. i had thought it was just the construction of the mirror but its not. i came to that conclusion because the same thing happens when i check in a mirror that i have on the wall by my front door which leads directly outside. i attached a crude diagram to show what i mean (the yellow arrows represent the sunlight coming in).
i dont know if its an attachment issue, the glue or the edge of the system, which is swiss,but i have not been able to conquer it yet. direct light, sun light etc it cant be seen.
perhaps this is also what happened here. most people wouldnt be looking for anything but he was.
maybe like you said you need to let your sides grow out more? perhaps thats what caught his attention?
you made a post recently after getting a new piece and i had made a post to that thread with some suggestions. but for some reason the thread disappeared and i dont know if you ever saw it. perhaps the things i noticed where what he noticed?
i've looked at other pics that you posted in 2011they looked fantastic