Could be, but I don't think the report shows that. In fact it states:

"Many scientists, both critics and supporters, have expressed concern that the experimental methods we have used have not adequately established that causation exists between IQ and infectious disease, and that its direction is the one we predict. The use of longitudinal studies could answer all of these questions. Such studies would track children from as early an age as possible, documenting the intensity, duration, timing, and types of infections they acquire, and track their cognitive development through the use of culturally-appropriate IQ tests."

In fact I'd think that so many other potential causative factors, such as lack of education, freetime, skilled employment etc. are likely to be correlated with incidence of infectious disease, that it's hard to draw any strong conclusions without a more detailed study.