The first says, we did something bad, but it was justified, i.e. we didn't do anything morally wrong. The second says we did something bad, we thought it was justified, but it turns out that it was a mistake. Einstein is clearly expressing the latter, whereas official American policy expresses the former, and there has never been an apology.
Presumably you have a proposed option to have done that without atomic weaponry and that the Americans should have recognized with the information available to them; what is that option?
Instead you get "we did what we had to", which is unapologetic, and doesn't allow the possibility of there being better options. It basically comes down to admitting doubt vs. reinforcing belief (since asserting an unfalsifiable claim is a belief).
Nevertheless, I'm not convinced that invading Japan was the only alternative. I mentioned somewhere, perhaps not in reply to you, that dropping atomic bombs on remote regions of Japan would have demonstrated military superiority with far less casualties.
And another post in this thread linked to this article:
http://www.foreignpolicy.com/articles/2013/05/29/the_bomb_di...
If you're actually really interested in this, and maybe you are since you're obviously interested in military stuff, I'm pretty sure there are entire bookcases filled with books and journal articles weighing the pros and cons of the decision to drop the bomb.