I really don't think that's the case here. I think Comey was in a damned if he does/damned if he doesn't case.
He opted for the most transparent option. I think he made the right call, but he's getting skewered over it.
He explained in his letter they don't know what those emails contain. Just that they found emails. The problem is people fill in the blanks with their own bias at that which is dangerous. That's what Trump supporters are doing when IMO they shouldn't be. Because now what happens is lets say they check all the emails out and find nothing. Then the right says there's a coverup or shennanigans going because "clearly there was something in them otherwise they wouldn't have looked into it." And thats a very wrong assumption.
The other option Comey had would for him to not have disclosed anything until they actually investigate the emails. The problem there is certainly the Republicans would have found out and then flipped their **** at him for not disclosing because "he's trying to cover up/protect Clinton."
I think he made the right call so close to the election with being transparent. The problem is the right it reading way too much into his letter and assuming something is in those emails. There may very well be, but there's just as much of a possibility there isn't anything in them. And if/when that happens, I don't expect the right to look very favorable on Comey either. They'll probably be calling for his head like the left is doing now.
The dude is screwed either way.