They aren't really trying to be nosy. It's that, IF you ARE sexually active? There are certain tests that should be performed on you, on a regular basis.
Also, it lets the doc know if you're a virgin, and the use of a speculum would NOT be a "good idea"
So, no, not nosy, at all. Just trying to give good, all-inclusive, quality care.
p.s. Your doc is bound by a code of silence (Doctor/Patient Confidentiality) regarding your medical history.
Unless YOU choose to alert/warn others of fatal, contagious disease (AIDS, HepC, etc.), or life-threatening disabilities (diabetes, epilepsy, COPD, etc.) by bracelet, tattoo, micro-chip implant, whatever,
your privacy is King.