"OH! Is it a powdered donut!? Because that sounds DELICIOUS!"
Sorry for the late reply, sadly unlike all my other online accounts, DA seems to give no email notifications on comments. But yes, to me it is one of the cutest Twist moments. Short, but just too cute.
The reason, if I recall the proper wording, was that Twist was too grounded and would just end up making it hard to justify doing crazy things with the CMC. Paraphrasing of course, but essentially she already had her cutie mark, didn't let bullies get to her, so it was just too much of a problem to fit her in.
I do hear we are getting returning S1 characters though, so we might see that Apple Bloom probably isn't a complete jerk and still consider Twist a good friend. Just one she doesn't have much in common with anymore, as kids, this means they just grew apart to pursue different goals. (I don't actually think AB is a jerk, she's selfish, but just too narrow minded to see what she's doing most the times.)
But yes, The Cutie Pox has the best Twist face.