HPV is spread by skin to skin contact. The HPV that affects the genitals is different from stains of HPV that affect your fingers or legs or feet, etc. HPV is not spread just through sexual intercourse, it can be spread via various sexual activities. So even if a person (or a person's partner) is a virgin (vaginal), it is entirely possible to be exposed to HPV by other activities.

HPV can also cause problems within a month, or years later, or decades later. If a person has more than one partner over the course of his/her lifetime, then there is no sure way of knowing who transmitted the virus.

I hope that helps.