It's an often quoted statistic that has become folklaw simply due to its popularity and repetition. Unfortunately, the 'research' was based on only nine words communicating attitudes or feelings in a controlled setup.
So how much is communicated by body language in real life? As someone else has said, more than you think, less than the 'experts' would like you to think.
Most body language is also not universal but culturally acquired. Not only can interpretation vary between cultures, but NT/aspie interpretation can be different.
The biggest problems occur when there is a perceived difference between the words and body language. I suspect in this case, the NT gives too much weight to their interpretation of the body language; the aspie gives too much weight to the actual words. Don't aspies often complain NTs don't say what they mean while NTs complain we don't notice the nonverbal.