I think that this early in the news cycle, maybe certainty is hard to come by. I have a different impression about what's at issue than you do.
But let's look at what you quoted.
This passage does not say that no emails to or from Hillary were found. They said that emails relevant to the case (and hence having something to do with Hillary's server) were obtained during the (koff! koff!) weiner investigation.
I think we'll have to wait to be sure, but I think they must have found emails to or from someone using Hillary's server.
I don't know. I think it's good for the FBI to release the information now. If they didn't, then they would have been accused of influencing the election. If they do, they are also accused, but I think the accusation is stronger if they postpone relevant information rather than if they release it when they would if no election were happening.
It's a somewhat bad effect for Clinton's campaign, but I think the FBI's decision is reasonable.
That said, of course the US attorney you quoted who said no announcement was necessary knows rather more about this stuff than I do.