Intervocalic alveolar tapping is definitely not just a California thing. I know that it even occurs in Canada, because in one of my classes we talked about a vowel change in some parts of Canada that keeps words like
writer and
rider distinct even though tapping occurs in each. I can try to dig up some more information on it if you'd like, though it might have to wait until I get home.
Personally, I think that just about any time someone says something like "The standard American accent they use on TV comes from [insert place here]," you can pretty safely dismiss their claims. As I uunderstand it, there has never been any particular regional dialect that actors aim for—what they aim for is to
lose features that are particular to regional dialects. According to my ear, even actors who play Californians (and possibly really are Californians) don't sound like real Californians.
But I suppose you could say he's at least partially right. The Midwestern and Western accents are
very similar—I don't even remember what the differences are. So any actor who strives for a perfect standard American English accent might sound like they're from California or the Midwest or anywhere in between.