Hola Tom

yes, you're right. The letter C sounds different depending on the vowel that comes after. 

C + a, o, u  sounds as [k], like in English words cat, cake, come, cucumber...

C + e, i sound as [th], like in English words the, thing, Athens...

In Spanish for example:

casa = ka-sa

coche = ko-che

cuna = ku - na

cine = thi -ne

cena = the-na

cien = thi -en

When the letter c has the sound of an s as in English words sound, Sally, soul..., this is in Latin America and some parts of Spain where people pronounce what just explained above related to the th sound but making a s sound instead of th. But this is not noticeable from the dictation because the narrator is from a part of Spain where the usual sound is th.

I hope this clarified it

Saludos

Inma