Listening to these words that seemed to be either a threat or a warning, Du You curled his lips. He was the type who would take things easy but not bow to pressure; however, he knew this was also a necessity for the job, for the good of the Earth as a whole.
So, in Du You's view, he probably had no choice but to swallow this resentment.
Although Du You was one to hold grudges and seek revenge, he was not unreasonable; such substantiated, harmless matters would probably only get his support, even if he knew about them. Frustrated, Du You was in no mood to open the Light Ball and treasure chest, and simply flew back with his two companions.
On the way back, Du You remembered these items. When he opened the Light Ball, perhaps because the Dragon King had already given him his share of benefits, there wasn't much of interest inside, leaving him with misplaced anticipation.