To be “closely held” means that a company’s shares are held (and often traded very thinly, if at all) by a small group of interested shareholders (quite often the founders/family). Since this is characteristic of smaller, private companies, Schweser may be generalizing by saying that closely held companies are private. There are rare occasions, though, where closely held companies are publicly traded. So while Schweser may be wrong here, if this statement mirrors the CFAI text (and I haven’t checked if it does), just go with it. When in doubt, the CFAI is right - while you’re taking the exams.