Correct If there is dust then either the seals are compromised so it's no longer water resistant or it has always been there from the factory or last intervention/service.
But tiny specs of dust can appear during manufacturing or from the lume application breaking apart over time. Happened on my AT recently. Tiny dust appeared on the dial, they weren't there before this, which they assumed were from the lume. Thankfully the watch was still under warranty and they removed the dust particles at no charge.