YDKJ: Etymology of whoopie pie

Taking my treat from the bakery lady, I hear her mutter, “I don’t know why it’s called whoopie pies. They’re not even pies.” Curiously, NYTimes.com:
Food historians believe whoopie pies originated in Pennsylvania, where they were baked by Amish women and put in farmers’ lunchboxes. Tired from a morning’s work, the farmers purportedly would shout “Whoopie!” if they discovered one of the desserts in their lunch pails.
Ah, but pie? Whoopie sammich?





