Like all surveys, it depends what you ask and when you ask it. Is the questionnaire published, it should be for a reputable survey. What was the sample size, it really needs to be more than 1000 to have much statistical validity.
But who cares about all that it can still make a good (or bad) story, depending on the results.
It's not hard to find out from the National Rail Passenger Survey pages of Passenger Focus. That says:
27th June 2019
Transport Focus consults more than 50,000 passengers a year to produce the National Rail Passenger Survey (NRPS▸ ) – a network-wide picture of passengers’ satisfaction with rail travel. Passenger opinions of train services are collected twice a year from a representative sample of journeys.
Passengers’ overall satisfaction and satisfaction with 30 specific aspects of service can, therefore, be compared over time.
NRPS is the largest published rail passenger satisfaction survey in the world. It supplies an official statistic that is used as a key performance indicator in most rail franchises.
Latest results
To read results from the NRPS spring wave 2019 undertaken between 04 February and 14 April 2019 download the full report or at-a-glance guides for the entire rail network and each train operator
There's a bit about methodology in
the main report, though apparently not the questions - but I think there isn't much to know, it's "how satisfied are you with" a long list of things. There is a link to more information, but it goes round in a circle; probably something is still on the site but with no link to it (all too common these days).
But really the misleading bit of the article was to call them "new figures released by Great Western Railway...".