The testing is pretty complicated as far as I’m aware. They remove samples of different microbes from the stool sample and culture them in a lab and then measure the CFU/ml. I don’t think it’s always 100% accurate and the rates probably vary lab to lab, but more than 10^4 CFU/ml was considered significant in this study, which is worth reading if you want to know how candida is measured. There are other interesting tidbits in there, like the fact that 5% of controls had colonisation in the stomach. Even if it isn’t 100% accurate, I’d take it as a great sign along with a reduction in symptoms.