OK thanks guys, I understand. If I sum it up: for someone who doesn’t have a Thai bank account (so only foreign accounts), the money considered as remitted corresponds either to the money spent in Thailand (regardless of the method) or possibly to the cash brought in physically. I don’t see any other type of remitted income apart from that.
Thanks for the clarification. However, the definition of “remitted” is still a bit unclear to me — especially when you don’t have a bank account in Thailand. I’m not sure what it actually means. If “remitted” simply means “money spent in Thailand,” then that’s easy to understand. But if not, I’m confused about how it’s defined.
Okay, thanks a lot guys! So, to sum up: it's difficult to open a bank account, and I will indeed become a Thai tax resident if I stay more than 180 days in the country. That's the information I needed — thanks!