There are many ways in which someones body communication or delivery can contradict the message or spoken word that is being presented. For instance, if someone is presenting a message or speech that is exciting and really up beat, but he or she is just standing there with a straight face and no movement of the body, their body communication is leading towards serious or perhaps even a sad message. This contradiction of message and body can greatly impact the message itself, but also those listening. It can be both a distraction or can lead those listening to get the wrong idea of what is being portrayed. It is very important to make sure that ones body communication is on the same page and track as the message that is being presented in order to arrive the best possible outcome.
I like your connection between a speaker using appropriate tone to match the scenario, and I agree that a somber speaker would not be able to relate to a happy crowd.
When you mentioned it being a distraction, I came to the realization of how important it is to match what you are "preaching". If the audience is distracted, then the message cannot be as effective.
I like the example you gave! It clearly represents the issue and helps me understand better what the question was asking.