Thanks, arturo. Nevertheless, simply reverting the global state by calling ofSetRectMode(OF_RECTMODE_CORNER) in the end doesn't do the job; it seems to affect other drawing functions outside of this one.
As an alternative, I would translate the view by -arrow.getWidth()/2 and -arrow.getHeight()/2 before rotating, so the centre is at the centre of the texture. Nevertheless, I don't get this to work in the code above, with the explicit position at x,y.