Prefacing by saying I don't think he should have popped off to the media.
That said, he's been playing some of the best basketball of his career this year, shooting-wise, and it's not close. At the same time, he's playing 10 minutes fewer per game this year than he has for his career, and several minutes fewer than he did last year in a similar guard rotation. Presumably he worked very hard on his shooting this year to improve it, and feels he should get more minutes, because he's been a good soldier, and again, is playing very well. Meanwhile, he's been in trade rumors all season long, and especially this week. And soon Rondo will be back and he might be cut from the rotation. The frustration is understandable, if, again, annoying.