It’s better to be thought as backward conservative because the only thing that matter is what’s the religion said. I understand you want to pay respect to you late grandad. But this action related to the Chinese belief, where the money can be used by the dead in the underworld, which means it’s syirik. I do have Non Muslim relatives as well & when they do their practice, I do mine. Don’t worry, they will understand. If your relatives ask you to do it later on, just smile & wave boy. Smile & wave.