Having some priests be literate does not mean that Israelites in general were literate.
1. Your post interjected the term "in general" into the discussion. It is neither implied nor inferred by the article.
2. Neither does a single tablet containing a curse mean that the Israelites "in general" were literate. Nor is it any any indication that the curse was not written by a priest, who might have been one of the few who were literate.