Exactly.
The constituency had been Labour since 1987 and Wallis only served one term before it turned Labour again.
Years ago there was a similar situation Montgomeryshire. It returned mostly Liberal MPs for a century from 1880 (Clement Davies was variously Liberal, National Liberal and Independent) until Maggie's victory in 1979. The Conservative MP was a common or garden doofus, who managed to alienate so many people that the constituency returned to the Liberals in 1983, in the teeth of a Tory landslide.
(Mind you, the Liberals chose Lembit Opik who won in 1997, but lost in 2010 to the Tories.)