Actually, that's incorrect.
If you delve deeper, beyond the often unreliable world of Wikipedia, you'll see the dialect is referred to as Isaan Laos.
This is on order to distinguish it from several other dialects spoken in the region, including; Northern Khmer, Gui, Thai Korat, etc.
Historically, Isaan Laos isn"t the oldest language to be spoken in the region, since it was annexed by the Siamese, hence its name referencing both locations (Laos and Isaan).