Actually, yes. Like all communication, there are multiple levels, including context. Magicians, comedians, and similar performers are VERY familiar and in tune to it with it when it comes to laughter, but so is almost EVERYONE in any other situation. You understand people's laughs every day well beyond 'they must think something's funny.' You make the exact distinction you mockingly presented, all the time. You generally know, in your daily life, very clearly when someone laughs because something was stupid, or in disbelief, or at humour, or at an awkward situation, etc. Laughter goes FAR beyond just being a reaction to humour. Why? Well, because they didn't, because it wasn't a joke.