This is so simply not true, or highly subfield-dependent. Unless you are a superstar, there is no way you get a TT job without a postdoc in math.
Seeing that my institution and lots more do have assistant professorships for new PhDs in math, and I even have friends who have attained such positions, this is very much true. Of course one needs to be relatively successful.
Edit: Okay, it appears that some people consider those positions “postdoc in disguise”.