They only have the picture on their website and I'm about 98% certain that it's just a stock photo and not a snake currently in anyone's possession. All talk of northern garters, WC etc. is pointless.

There's not one hint of either parietalis or radix in that picture. The supralabial markings and lateral stripe are nothing like what you'd see on T. radix, the dorsal stripe is wrong for both parietalis and radix. It's not even close to semifasciatus.

Find a picture of a properly identified snake that looks like it, if you think you know what it is.