It’s a cheeky play on “WINdows Emulator” as well as “WINE’s Is Not an Emulator”, but I think for both legal (trademark) and logistical (it really isn’t an emulator) reasons, you’ll never officially see that bit sanctioned
Pine was already taken by an email reader. One of the early ascii email readers was called elm, for ELectronic Mail. Pine was made after elm and it stands for Pine Is Not Elm.