> These results showed that most of participants who were aware of their toxoplasmosis status (and nearly all male responders) had been tested for toxoplasmosis in our lab.
So they only had a confirmation for the positive/negative cases, but they have no way to confirm that the ones who say "not sure" were accurately reporting their answers. That's a pretty big gap they use to draw conclusions.
most of participants who were aware [...]
had been tested [...] in our lab.
They can test samples drawn expressly for the experiment, and not inform the individual, and then still use the lab-verified determination of infection status in the results. They can take blood, find out, and not tell the people if they are infected, even if they didn't know, and let them stay infected without knowing.
> The major limitation of the present study is that it is based on self-reported information on subjects’ sexual life and self-reported Toxoplasma infection status.
They go on to caution against overgeneralization based on these extremely specific and inherently uncertain results, which is entirely reasonable, but I think it's rather hasty to write off the study as "junk". At the very least, it's better and more careful science even despite its limitations than one ordinarily sees performed in this realm.