@yeri I am not sure if they were from a tech scene (they were all locals), but they had iPhones so we are able to message each other back & forth over iMessage.
The local expats I encountered definitely used WhatsApp, although all those with an iPhone definitely used iMessage with me when I was there.
It could simply be that they adapted to the communication device depending on the person (which is not unheard of).
I know people who use iMessage, Signal, WhatsApp, & Telegram.