The 54201-S0809LF: For a connector that may be disconnected a few times over its service life, that plating grade provides a reliable oxide-free interface. Surface mount termination means the header sits on top of the board with no through-hole tails — the solder joint takes the mechanical and electrical connection.
On the board, the 0.100" pitch allows two traces between pads on a standard 0.062" board with 8-mil lines and spaces, keeping routing density manageable. This sets the z-height clearance under the mating receptacle.