Reading a bit into “ended improperly”, one possibility of them saying good morning could be if after they stopped talking late at night you still added 10 or so more messages in a row. Hehe. I used to get that alot. Basically both sincere and sarcastic at the same time. To let you know they are awake now and caught up on your continued posts after they fell asleep, as well as poke a bit of fun that you maybe missed a “too subtle for us” hint that the other person was going to sleep before you kept posting.