As another Asian individual, I'd like to add to the comment from @Ambulocetus and also state that Yin/Yang is a philosophical / cosmological / Chinese medicinal concept rather than a religious one. While it has been used in religious imagery, it's not wholly tied to any one religion, and is in fact a concept that spans across multiple different cultures, and it's indeed incorrect to actually say it's religious by nature. It's actually a very large part of Chinese and Asian culture as a whole.
(For instance, as a whole, the Yin-Yang symbol can be referred to as "Taiji" - and you can even see this concept on South Korea's flag, known as Taegeuk (Taegeukgi), showcasing that it's not just from one specific religion.
https://en.wikipedia.org/wiki/Taegeuk)
Basically, it's cultural content, not religious content. I agree with the sentiment above that if this isn't allowed, then wings shouldn't be either because of their potential to be equated to a religious concept, despite the fact that wings aren't inherently religious imagery themselves, either. Or it's like saying you can't use stars in your designs, just because a religion might have star imagery or something. This decision seems out of place to me.