Did you know that Chinese didn’t have a word for “She” until about 100 years ago? In fact, Chinese operated without a female 3rd person pronoun for thousands of years, and it wasn’t a problem – until interaction with the west. Watch this video to learn the fascinating (albeit winding) history of Chinese gendered pronouns.
Exactly. It’s not the person speaking who is making the assumption about the subject’s gender, it’s the person writing the subtitles. The fact that they decided to go with the male pronoun for the trans person says more about them, the translator, than it does about the Chinese person who was speaking.