Well...: it's true, honesty is (almost) always the best policy. But here's the catch: in order for honesty to be integrity, the guy also has to take responsibility for one's actions. If a guy says, "I can't see myself with you for the long term," he also has a responsibility -- if he respects the girl, or hopes to be friends with her ever again -- to provide an explanation why. If he says, "I'm bored, and need to explore other options," he also needs to take responsibility for the consequences of that choice (causing girl gnarly, raw pain; girl losing respect for guy).
No doubt that guy was being honest; no doubt that he couldn't see himself with girl in the long term (he admitted as much). But honesty isn't really enough, if you respect the person that you're breaking up with -- integrity is also required.