In the science of sport podcast at around 1:05:55h Tygart says:
We'll have let's just ballpark 30% of our positive tests and up being innocent source positive - so meat contamination or water or kissing or intimacy or using your roommate's armsleeve or whatever.
Not intentional cheats.
One third of positives just from eating the wrong food or kissing is way higher than I expected it to be.
To be fair: The quote is with regards to regular untargeted testing - for targeted testing after an investigation he estimates that about all of the positives are intentional cheats.
I can't post links, so you'll have to search for it on Spotify yourself .