The throwaway comment about not using diagrams was truly baffling to me. A dashed arrow pointing in one direction is async data flow in that direction, A solid

The throwaway comment about not using diagrams was truly baffling to me. A dashed arrow pointing in one direction is async data flow in that direction, A solid arrow is synchronous, and a swimlane / activity diagram shouldn't have two-way arrows in it (what would that mean?). How is that more likely to be read wrong than source code? Doesn't match my experience at all.