Evidently BS felt the best way to capture Mat's humor was for him to be a gag comic or something. That first scene featuring BS's Mat was jarring, as RJ would never have Mat be so put out because nobody appreciated the aliases he came up with. That was very, very lame. Jarringly so.
He was to be either a comic character, or a rogue type one, always sauntering, gambling, drinking, etc. And Mat certainly always had all those traits in him, it's just that when RJ wrote him, they were not the entire extent of his personality and character.
Oh, and that reminds me of one other instance! A big one too. Mat riding out during one of the White Tower group's battles to lead an assault himself. The real Mat hated fighting and had to be dragged into it. He wouldn't lead an assault by himself on a mere lark--not to mention that even aside from his personality, he always said that a general's place was in the back, observing rather than participating.