I spent a lot of time reading about this process and keep coming across references to its antiquity- evident source of what looks to me to be an erroneous presumption seems to be Wikipedia.
From what I've read, the presumed "father of Sous Vide" (literally, "under vacuum"), Sir Benjamin Thompson, is actually the father of CANNING. Which of course involves a vacuum, but one created at much higher temps that those used in the method described/practiced as sous videry. And which certainly revolutionized food preservation.
The low temp process now known as sous vide and not meant as a preservative method didn't come into use until the 1960's/1970's, when heat tolerant plastic bags began to appear. Initially the process was used in hospitals and other institutions to make food more consistent and palatable. The first use by a professional chef seems to have been by a fellow in France attempting to reduce losses when cooking pate de fois gras. He applied what he found to other foods, and a style of cookery was born.
The rest is history...but it's not ANCIENT history!