Never knew! This sounds weird for me, because teachers taught us that they/them used only for plural.

Superb, thank you!

I am a native English speaker and they/them being used in this way has become more accepted and recommended over time. I was taught explicitly not to do this when I was in school, but that was a few decades ago. Using he/him when gender is unknown or unimportant is regarded as exclusionary. Usually, it'a not an issue, but I find it does sometimes make things more difficult to parse or understand without additional context. In this case, there aren't really any drawbacks.