Assalamu alaykum
It's a very natural response, I think especially if you hear something you strongly disagree with, or is ridiculous or are not sure what to say, you just smile or laugh, like on the other side of the spectrum from a fit of anger.
Once, someone said something so utterly ridiculous, it was unbelievable, and not knowing what to say, and not being bothered enough to argue, I kind of laughed (and I didn't find it funny at all). Might be like hysterical laughter - it's a very unconscious thing though.
Altho when I am very angry (rarely, alhamdulillah), I cry. I hate that as well, but it's something beyond my control.