Didn’t the autopsy also indicate that Foster had engaged in sex with a blonde woman shortly before his death? There were some pubic hairs that were never brought up again.
I think you are thinking of the carpet fibers there were found on his clothing. And then there was the story back then of a WH janitor hauling a rug out of the WH. And then he retired and moved away somewhere and was never seen again. End of story.
That theory didn't originate from the autopsy, but rather from laboratory tests on Foster's clothing. There were semen stains on his underwear and blonde hairs on his clothing.
But there is an alternative explanation for that. Ejection of semen immediately after death is fairly common in men, and doesn't have to be caused by a voluntary ejaculation in life. The precise reason for this is not well understood, but it is known to happen.
As for the blonde hairs on the clothing, they could have been shed by an attacker in close proximity or contact.