Probably because they weren't around in 970 A.D.
In fact, wine grapes didn't return to the region until a gentleman named Merlin replanted them some time in the 600s. He'd earlier replanted the grapes in Brittany upon his exile from what was rapidly becoming known as England (due to Angle and Saxon invaders ~ and those folks just red like bunnies doncha' know).
To begin with, it talks as if it is a case from the present, but it is from 2003, when there was a record heatwave.
Also, this is an account from an inexperienced winegrower.
“We’d never seen anything like it,” says Christine, a 52-year-old mother of two, who took over the renowned Vernay estate from her father in 1997. Nothing like it since 1997! A very long time.
One can tell she was inexperienced, that she took a vacation in the middle of August. A winegrower stays around in late summer, watching every day, they don't go on holidays. At the slightest turn in the weather - early ripening, a heat wave, a pending hailstorm, and they have to rush out and start harvesting. If she had been there and done that, at the start of the heatwave, she would have been in a better position.
... a friend from the same village, Condrieu, called her husband’s mobile phone. “The grapes have ripened early. You need to come home now,” he said.
That sort of thing is why winegrowing is a dreadful job. One can work all year, then lose an entire harvest within 12 hours, if the weather turns.