[Dragbat]

It is pretty normal, mainly because it doesn't constantly take into account that it's an AI when generating text and it's basically predicting the next most likely token, so if it said something like "After reading that, I was literally smiling", when it finishes "After reading that, I was literally" it has a few options of what to continue it with.

If the previous chat was something that would cause a regular human to smile or laugh (a behaviour existed somewhere on its training data), then "smiling" and "laughing" are probably the most likely next tokens to express humor. Similar could be said about topics other than humor.