Upon returning, Garth'zel gives Ezra a patient look. "Aside from the fact that you are far too young for lying to me to work very well, One of the things I learned how to do with the Force is to heal. Specifically, as many illnesses as I could although I've mostly found myself healing various types of injuries instead."

In other words, he would potentially know even before Ezra does if Ezra's sick.