The P20 isn't actually the fertilizer ingredient - it's complicated. I don't think it is plant "doping", it could be a perfectly normal result. A test like that wouldn't normally be done in soil but since I can't see how they did it I have no idea what they did. But, with plant nutrition there is a thing called the law of the minimum. That means that if any of the essential nutrients is deficient then it doesn't matter how much of the others you give it, they will be limited in performance by the deficient one. When you grow in pots you are the one who must make sure all the essential nutrients are supplied in sufficient amounts. If the "common fertilizer" only contained NPK and not any micronutrients, then it is normal that the one with the micronutrients would do better unless there's some other source in the growing mix that applied to all of the pots. So the better performance could just be the result of supplying all the nutrients the plants needed whereas the others didn't. (Although calcium and magnesium are not supplied in the fertilizer, I don't know what they did about those).
