I do that a lot when people send me stuff. Like, it's a picture of a funny quote, all I have to say to that is "lol" or "haha" or something. Likewise, if you send me a message that you're doing something, that doesn't open up for any conversation, then I'll just say "I see haha" or something equally conversation-ending, because to me that conversation never started in the first place. What am I supposed to say to "I'm at the car wash right now"?
And then sometimes I wish people would just take the hint and stop messaging me if that's all I respond to them. I'm not going to say "listen, I don't want to talk to you because _____, so please leave me alone" because that usually ends in argument about how I should want to talk to them, so I hope I annoy them enough with one-word answers to make them leave me alone.
I do this. Those messages, when attempting to start a conversation don't really do that at all. It's like you're tweeting at one person. Can't really think of any other way to reply.
While I'm guilty of being on the other side of this situation as well, it's generally, on my part, in attempt to revive a conversation once small talk and open dialogue seem to be in a lull. A kick in the pants. Not entirely effective, I've since learned, but well-intentioned.