no the arrows don't mean much. they just show that a pressure has been applied to an entity. the number and placement ofht arrows is a function (I am guuessing) of the edges bounding the surface patch or soemthing like that. they could have a much better algorthim for that.
You assumption about what you should see is not correct. You may have a uniform traction but what you are showing is the most compressive stresses with P3 and you have bending and Poisson's induced effects due to the shape and the restraints. Try a flat plate with well thought out restraints and you will get what you assume will happen.