The summons was clear and simple: you were needed for a simple task of exploration in dangerous territory. Large payment was mentioned, with possibility of even more. It seems your employer's letter only let out a few important details. A Pathfinder adventure for 3rd-level characters.
Hej Jeff - yes, I got that one. It's confusing nevertheless. Why not opt for s/he instead?
Because it was supposed to confuse the players, though not necessarily the GM, and reflect the ways in which the character's appearance and gender were highly mutable toward one or the other rather than indeterminate.