You simply couldn't know for sure whether you caught it from him or even whether you had the same disease as him. I sat next to kids in classrooms for decades and was coughed over and sneezed on and handled their snotty books many times. I rarely got ill and there was not one single occasion on which I could attribute any ague I picked up to any particular pupil. You have a habit of making things up and/or expressing conjecture as certainty. That's all.