I've had this happen a while ago, but completely forgot about it until recently.
It was a "preview" screen of a message from a Whatsapp conversation.
I've been trying to figure out how to get it to work again. I'm not sure if it's limited to Whatsapp because I believe it is also possible with SMS texts. The preview is just a screen that shows the message and an "OK" button (I think).
One of those "gotta know" things.. and it's killing me that I can't figure out how to replicate it! Anyone know what I'm talking about... or am I going crazy? :/