[Ken is immeasurably pleased by the praise, not so much because he doesn't know Mukuro might be exaggerating (at the very least) but because he does. Whether or not Mukuro's eating much of it, whether or not it's actually good, Mukuro is saying Ken did well. So either Ken actually did well enough for Mukuro to appreciate, or Mukuro cares about him enough to want him to feel like he did.

And while Ken would vastly prefer to actually do well by Mukuro than have Mukuro humor him, he's fully conscious of the fact that Mukuro hardly cares about anyone - that people Mukuro would ever bother to humor could likely be counted on one hand with fingers to spare. That, if Ken's receiving any consideration at all, it's a massive indicator of esteem from one of the only people in the world whose opinion matters to him.

So to Ken, it doesn't matter if Mukuro is being entirely truthful or not. He's happy either way.]

Oh, there's plenty left, byon. [Ken's eyes gleam.] And I'd just make a mess out of other things if there wasn't, byon. Kakipi says I can make a mess out of thin air.