The stock iOS keyboard also does this.
It used to be that emoji were just to express some feeling that would otherwise take a lot of words, or to disambiguate statements that could mean different things in different context (sarcasm/irony, jokes, etc). Emoji are are very useful for that. Like the parent I replied to I don't understand the use case for almost all of the other emoji.
It's interesting because it's no longer just filling a gap in textual communication, but using textual communication to express a thought or joke that you can't really express with the same interpretation in any other conversational medium. Responding to "and Dave will be there" with blank-stare + man-fleeing expresses something you could only really express otherwise by drawing a comic strip on the spot and handing it to someone.