He probably didn't want to be there making said banner, so he was in a negative frame of mind and woulnd't have been happy with even the most beautiful banner on earth (which is probably what your suggestion was!). What a grump. Let's try to chalk it up to him having a bad day, with maybe the possibility of him preferring the money was being put towards things other than a banner, which is why he was grump about being there.
Edited to add that nothing excuses his GD'ing though.