You've almost answered the question yourself.
Noise cancellation only on the microphone. This means that the person you're talking to can't hear all your background noise.
You can only achieve noise cancellation on your ears (i.e. on the speakers) with a closed design, which is exactly what the OpenFit are not. They lie open in the ear canal and fill you with music. You can hear everything from your surroundings - unless you have turned the volume up to full - precisely because of this open design. The "transparent" mode is always on, so to speak.

That's what I thought too, but galaxus writes it down for the black ones and doesn't mention it for the beige ones.