Obviously as a Celtics fan I like Rondo, but it's pretty clear that he's making excuses on this one. "I was homesick"? Says the guy who travels on the road for half of the year playing basketball? Get outta here.
That, coupled with the fact he's written off any possibility of joining Team USA in the future, tells me he left because he knew he'd get cut.
I don't doubt that he likes his summers and he doesn't view it as a big loss, but he knew he'd be cut so he bolted before it happened. People don't just go to Greece for a week and get "homesick".