Smiling seems to come naturally to humans. It is an expression that crosses cultural divides. However even on earth there are examples of species that show their teeth for a completely different reason.

Expressions of meaning (whether they are visual, audible or some other method) must have a shared experiential background, whether that be shared language, cultural overlap, or whatever is necessary for the reception of an idea that translates as intended in the other beings thoughts. Sometimes ideas get lost in the process of expression or reception. Unfamiliar slang or idioms and dialectical difference, can muddy the waters of same language speakers. Different subcultures express different body language meaning different things. Even under the best of communication situations deeper meanings in metaphor or allusions may be missed or misunderstood.

Bear that in mind next time you bare your teeth.