I think in a technical context, it always has the meaning OP is talking about. Check out https://en.wikipedia.org/wiki/Transparency_(human%E2%80%93co.... I've mostly seen research papers use transparency with this meaning.

No, he's talking about sugar that looks like this - https://www.gomothers.in/store/garg-traders/product/sugar-lo.... It's small enough but clearly distinct from salt