Do not know with accuracy the scale USDA. But I believe that z6 must be a very cold temperature for the Camellias.

You should read the work of the Dr. Ackerman. he was employed at National Arboretum in Washington D.C.,
he is recognized throughout the world by your works on Camellias. Specially on Camellias for places of very cold temperatures.

You can read your work in the Optional LINK.

Pardon for my evil English.
Regards.

Here is a link that might be useful: Winter'sCamellias Dr.Ackerman

As I mentioned on a recent post , I keep mine in containers , which come indoors for the winter, and I do think those garden centers "push' the hardiness thing with some plants they sell, which are suitable only for a zone warmer that the store they're somtimes sold in. Best to research particular plants before buying them sometimes, though I don't always follow my own advice!! I'd be happy to see camellias offered here as container plants, though I"d think they "should" warn folks in our zone 5-6 that they may not be reliably hardy through the winters here!!