I am not saying that the guy is wrong and am not looking for an argument. I don't quite own all the sources which he quotes and don't have the time or interest in pinpointing when and where a particular chord sequence was used or who first used the term blues. We will never know for sure it's all so long ago.
As I stated above the region generally referred to among non-laymen blues followers as the Delta in Mississippi is that north west corner, some people would also include that part of Arkansas just across the bridge.

As a non-American I am surprised to hear that the geological Mississippi Delta starts in Ohio. But I am more interested in music than geology.