In BIR terms, which is what we should be thinking about, coconut flour is more than likely what they use, coz it's cheap. Coconut powder as in coconut 'milk' powder, would not be used, coz its expensive!
I think based on that logic, coconut flour is the one, even if it sometimes gets described as coconut powder. It is powdery in appearence but not as silky as normal flour in texture, hence the grainyness that you get in BIR CTM or Korma.
If anyone is in doubt of it, leave your CTM or Korma to go cold. You can almost see the texture that the coconut flour adds to the dish.
Im pretty sure that 'most' BIR's don't use coconut milk either, so why would they use coconut milk powder? I've known them to use cream or bog standard milk, and even heard of them using evaporated milk, but never coconut milk! Seems more of a Thai thing to me!
Ray