Utter rubbish. He probably supported them as a child, as did you with Cardiff. I can't say that as an absolute certainty but it's a pretty good assumption to make. Very few people around Geraint's age supported Cardiff, I'm of a similar age and I was the only City fan in my year at school.
Also, Bale hasn't mentioned us either, so why should Warburton or Thomas? By the way...
https://twitter.com/GeraintThomas86/...32214987739143