back in the day, as in way back in the day, when i learned english (in two different english speaking countries) i thought i learned that when a singular person of unknown sex was referred to "he" could refer to either sex.
however *main memory checksum error* so..
You must be older than me... When I was ESLing I was told to use "he or she" but apparently it's deprecated too now. Which TBH is fine with me. Never made much sense anyway, e.g. why not "she or he"? "They" is shorter and more convenient and anyone bitching about plural shalt read some Shakespeare.