Stumpy being mad at Kaeloo and Mr. Cat more than anyone else makes sense when you consider that his mother is extremely neglectful of him - the idea of Kaeloo and Mr. Cat, who act as parental/older sibling figures to him and Quack Quack, ignoring him is very hurtful.
Not to mention that Quack Quack is Stumpy's best friend, and this is one of the only occasions where he does anything bad to him. Kaeloo and Mr. Cat, on the other hand, have been assholes to Stumpy ever since the series began.
Stumpy ends up in a feud with his friends because they refused to play Me-Me-Nopoly, a parody of Monopoly, with him. Later in the episode, he punishes Kaeloo and Mr. Cat by forcing them to play it with him. Monopoly is known as a game that ruins friendships, after all.
