As if you don’t use the buttons on the toolshelf, all you need is to hold D and mouse click around to draw with the grease pencil, you probably accidentally pressed D in edit mode while clicking somewhere.
The grease pencil strokes are associated with the current active object. If you duplicate an object with grease pencil strokes this new object will also have those grease pencil strokes. If you change the outliner to Datablocks you will be able to see that one of the objects datablocks is the Grease Pencil Data
well i think i was working on some cycles file a few days ago and i set some default parameters for cycles
and for what ever reason greace pencil was also set and save it Ctrl-U
now i corrected that in my default file and gease pencil is out now!
i did not use D key
but did shift D to copy the object
but should this leave behind a black dot !
just tried again to redo it and it does not do it anymore
will try some more this later on to see how to repeat this behavior!