The comment lives in between two worlds. For one it refers to objectively measured data in a well controlled environment, second it refers to subjective experience under utterly uncontrolled circumstances. Third you just speculate on something not measured, the current noise, which effect again depends on unspecified, widely varying properties."My iFi Zen Phono has almost no audible background hiss with either MM or MC cartridges, but its SINAD was measured to be comparatively poor."
This is exactly what I'd expect if you measure SINAD by shorting the input. SINAD measured with the input shorted is no predictor of performance with an MM cart attached because the biggest noise contributor - input noise current - is not present.
If you like current noise to be specified, I support the inquiry.