Welcome back to the forum.
This is a good example of the problems that can arise when anxious persons seek unnecessary STD testing. The HPV tests are not recommended by any responsible health authority (health departments, CDC, STD/HPV experts) for testing in this manner, especially by men -- even though many labs offer and market them. The first caution is that the performance of the tests isn't completely understood, and not all positive results are truly positive; you may not have an anal HPV infection at all. Also, the negative genital area testing does not rule out the possibility that you in fact have genital HPV. The available tests do not detect all infections. Indeed, HPV researchers disagree on the best way to collect genital specimens in men to maximize test sensitivity -- and whatever method your lab uses probably doesn't detect all infections.
But if you do have anal HPV, it probably will never mean anything important. Strictly heterosexual men get anal HPV all the time -- not as frequently as women or as men with rectal sexual exposure (mostly men who have sex with men), but still quite common. The exact origins aren't known, and it's almost always unknowable in any particular case. Self-inoculation from genital infection probably accounts for most cases, and you could have had a past genital infection that was the source of the anal one, with the genital infection having cleared. This undoubtedly is more likely than the oral exposure 20 years ago or from a massage. That you are generally healthy is great, but such things have absolutely no effect on susceptibility to HPV or in how well (or how rapidly) the immune system clears HPV infections.
So it was a mistake for you to be tested -- nohting can be done about asymptomatic HPV infections, and nothing is known to further reduce the already very low risk that such an infection will ever cause an important health problem. And as noted above, HPV testing undoubtedly misses many infections, so a negative result isn't necessarily reassuring. Therefore, why test?
However, now that you have done it and have the positive result, it would make sense for you to see a doctor experienced in anal and rectal HPV infections, such as a proctologist or colorectal surgeon. (Your PCP probably can refer you to someone.) Such a provider would probably examine you closely, including anoscopy or proctoscopy (to look inside). If nothing abnormal is found, which is what you should expect, perhaps another examination or two over the next couple of years.
I hope this information is helpful. Let me know if anything isn't clear.