No, you're completely and utterly missing my point. If Rick tells the others what the CDC guy told him, which is likely that everyone is infected, that group will lose all hope of a better tomorrow.
It's possible that the group would react much worse to this news than we are. They're in the middle of a mind-bendingly hellish situation, and we're just typing away from the comfort of our parents' basements, without so much of a waft of ice-hot zombie breath on our necks...so we can afford to be pretty blase. What's their problem, humanity has survived worse, get a grip you wimps.
But here's the problem: the storyline is not being judged by how the characters react, but what the audience thinks of it. If the audience sees a plot twist and thinks, pfft who cares, then it's a bad plot twist.
If that plot twist turns out to be true, it's got two strikes against it: the audience has already figured it out (some surprise) and has already found reasons to reject it.
Part of a storyteller's job is to know how the audience will react to a story - and hopefully to come up with twists the audience cannot predict.