H90,
I believe your captain was correct.
Airbus have published takeoff performance data for dry runways, and also for wet runways (which are runways that are covered with less than or equal to 3mm of water, slush or snow etc). Because damp runways fall within this very wide spectrum of runway conditions, the conservative approach taken by Airbus is to use wet runway performance data when calculating actual damp conditions.
The definition of DAMP, and the performance basis which should be used, are stated in FCOM>PER>TOF>CTA.