The bomb is unnecessary - if he wants to say it in private, it’s up to him, but you don’t do that when speaking to supporters.
As for why he said it, all I can think is he’s conveying to the bern’s young voters that he speaks their language.
But what is his point in saying he’ll bring American businesses back and then tell them that?
Is he saying...
...they won’t make money here because Americans won’t pay the prices...
...but if we want them here, he’ll certainly make them return?
I take it as “you still got some explainin’ to do, Lucy.”