I assume this is based on the CDC recommendation which doesn't seem to be based on any scientific research. On the other hand, this study finds that valved masks are as effective as cloth masks as far as leakage is concerned. (1) Also, I would assume a valved mask covered by a surgical would be ok (doctors and nurses do this sometimes) but that's not clear. Otherwise, they are asking people to wear less protection based on nothing but conjecture.

(1) https://advances.sciencemag.org/content/advances/early/2020/...