Questions & Answers about El remitente es chino.
Because remitente is a noun that can refer to either a male or a female sender. In Spanish, this kind of noun is often called a common-gender noun.
- el remitente = the sender, if male or unspecified
- la remitente = the sender, if female
So in El remitente es chino, the sentence is talking about a male sender, or a sender treated as grammatically masculine by context.
Because ser is used for things like identity, origin, nationality, and permanent characteristics.
Here, chino means Chinese, which is a nationality or origin, so Spanish uses ser:
- El remitente es chino.
Using estar here would sound wrong in standard Spanish, because nationality is not treated as a temporary condition.