Read further; the subjects of this study were also examined and had labs drawn which included a toxo test, and were issued unique codes which they provided with their study responses:

> At the end of the questionnaire, the participants could provide their unique “guinea pig code.” Because of the rather sensitive sex- and health-related contents of this questionnaire, it was “signed” only by 8% of the responders. However, other questionnaires distributed in this community were signed by most of responders (Flegr & Hodny, 2016). 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.

Unless I'm badly misreading the paper, they were therefore able to correlate study responses with confirmed presence or absence of latent toxo, with a high degree of specificity. It's odd that they would also include a question on the same subject, and I'm not competent to evaluate their methods of statistical analysis, but even the attempt to correlate study responses with laboratory data puts them head and shoulders above pretty much anyone else I've seen publish on this topic.