So Before You Say It Can't Happen, I'll Just Tell

So before you say it can't happen, I'll just tell you I know someone who does not use marijuana who failed a drug test for THC after swallowing the semen of someone who has been smoking pot as a sleep aid. That being said, I am just trying do some research in aid of defense for said person, who at the time has limited contact and research resources. so I'd just like some sort of relative specifics as to the levels that might show up on urine test, as I know that the sample was a high enough level for a "positive" result after being sent into "the lab", but I don't know what that level was, (& a sample taken the next day had a "negative" result), as there are many types of tests used, levels tested for, & different levels set to determine pos./neg. for different purposes etc. I also don't know for sure but would assume said person also engaged in unprotected vaginal sex in which ejaculation of semen occurred. (Said person being female)...?