Earlier quoted context omitted.
Could you please give an example of a word where th is hispanized as z?
The phoneme 'th' does not exist in Spanish. So, we tend to mispronounce it. Many of us, at least for the native European Spanish speakers, pronounce a Spanish 'z' instead of 'th'. By the way, the spanish phoneme 'z' is pronounced differently to the english phoneme 'z'.
We can do that in "think" or "thanks". But not in "they". In the latter case we tend to mispronounce it as a Spanish phoneme 'd'.