That means what I said it means. Negative campaigns are dirty and draining and don't help advance anything but negativity and you don't win by convincing people that you're the lesser of two evils.
If he wants to tackle issues, then he should talk about them and not Hillary Clinton.
She's not wrong taking objection to his tone. Bernie's got a lot of supporters who, while it's great to see them riled up over the old democratic process, are pretty quick to get riled up on attacking a strong woman in politics. And he used to do a good job reminding them.
But civil's John McCain in 2008, saying "Barack Obama's a great man but someone I disagree with politically. The last democratic debate where he basically told her "shut up men are talking" decidedly wasn't.
Just because he isn't making comments to the level of Donald Trump doesn't mean he couldn't clean things up.