That is a total lie. Whether it’s a לאו or an עשה or a דרבנן (דת יהודית) might have various opinions, but it’s a real הלכה.
See אג”מ אהע”ז ח”ב י”ב who says it’s an עשה but says it’s to be צנועה.
https://hebrewbooks.org/pdfpager.aspx?req=918&pgnum=325
(It’s pretty clear to many, btw, that he would be mattir these shaitels as long as the hair is covered, even if they look realistic.)