Anogenital HPV is almost always sexually acquired, but many experts think nonsexual transmission of genital HPV does occur. Exactly "how" and "how often" is very unclear. There is no evidence to indicate that it happens very often, but it's difficult to be more precise than that.
Things are also fuzzy when talking about just what constitutes "sex." For example, touching, rubbing and grinding genitals together is a risk for HPV transmission, even if no penetration or vaginal intercourse occurs. Oral sex is usually thought of more as a risk to the one performing, so it's probably rare (if it happens at all) that someone contracts genital HPV by receiving oral sex. Little if any risk seems to stem from hand to genital contact, but who can 100% rule it out?
So, assuming everyone involved is telling the truth, or what they honestly believe to be true, then who knows how to sort it out? HPV testing done several years after the fact is of little to no value, as virtually all HPV infections clear and become undetectable in that amount of time.
I'm sorry I don't have anything better to offer but I hope this helps at least a little. Please post again anytime.