Similar experience in HKG or SIN, can't remember - boarding QF flights into Australia, travelling Y and queued in the priority boarding lane. It was quite funny actually
I was third in the queue and for some reason, the person & his girlfriend before me turned & said something that went "this is for biz class & FF passengers mate". I smiled and still stood behind the couple. I can hear the person whispering to his girlfriend about people like me using biz/first class queue blah blah ...
5 mins later, a FA walks down the queue, checking BP's and ensuring the right people are in the right queue. Took a glance (just a glance, not a look) at my Y boarding pass - signals me down to the Y queue. I later point out the OW-E status printed and says, "sorry, all good" and moves on
Boarding begins ... scan BP, beep. beep. Now we all know what that could be
Enter the flight, I turn left and the person & his GF turn right
c'est la vie