Typically, US does not comp upgrade ANYONE to/from Hawaii (w/the exception of CP - cert required), so without actually asking the gate agent for that flight, it is impossible to know why they were in F.

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I'm 27, and have been an elite on US since I was 10...(thanks Mom and Dad for the first 8 years.) When I'm not traveling for work, you will most definitely see me in shorts and t-shirt/polo shirt/Under Armor shirt in First Class...and especially if I'm jetting to or from Hawaii in F.