I think the th-for-s/z thing is more Andalusian than Castilian, but it has been a very, very long time since I studied the language in any formal context; in any event, it wasn't taught that way at my high school, so he doesn't do it. I had suspected, though, that someone speaking Spanish Spanish (as it were) in Latin America would be thought of as a bit posh, rather as American English-speakers customarily react to people speaking in, e.g., BBC Received Pronunciation.

--G.
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