I saw a clip of the movie they used a couple months ago and I've been hoping somebody would use it for something brilliant like this. Thanks for not letting me down, internet!
It's the break-off point of the comedy, kind of like... kind of what happens when that british marshall struts into a Monty Python sketch and declares it silly, or that "And now for something completely different" quote however it goes. As if the previous things you were laughing at were a token offering from the high-brow to placate the slobs in the audience going "hyuk," followed by a resumption of your previous broadcast viewing.
My guess: the abrupt cut to credits signals that this is just any old random moment on board the Enterprise.
It's a little like Garfield Minus Garfield, where Jon Arbuckle is essentially a crazy next door neighbor who leaves his window open, and any time you look you're likely to see him being unwell.