I am reading a philosophical paper at the moment where the author refers to a 'person' in his argumentation. At some point he refers to this 'person' as 'she' (example below), though it is clear from the discourse that it's neither man nor woman, just a abstract person. This is the example:

If a person speaks the truth, and we have good reason to believe sheknows what she's talking about, and moreover we have good reason to believe she is trustworthy, then believing what she says is a true belief grounded in good reasons--a form of knowledge, by most accounts.

Why she? (not they or he...)