Actually, I don't think it's an exaggeration at all. Given thousands of years for the butterflies to develop, even such a trivial event would have massive consequences.
IMHO, the problem with butterflies is that while they
can have enormous consequences, there is no reason why they necessarily
must. Trivial actions don't necessarily change anything significant in the long term. In the Caesar nose-picking example, it might only have an influence on subsequent history if it caused him or someone else influential to do something else differently, something more significant. Possible, but not necessarily probable.