RF PCB Design Basics
I believe the first image you posted is meant to accommodate a machined EMI shield that is screwed down.  You can see that it would provide EMI shielding as well as isolating the circuits from each other.  The metal is plated so it makes contact with the shield (maybe just ENIG).



The second one you posted is for a cheaper TI part.  It looks like this design could accommodate a soldered down sheet metal shield for EMI.  These are much cheaper and if this small can be placed during automated assembly.



It's easier to take off the more expensive screwdown shield, but you can get some sheet metal ones with pull off tops.  They also make board clips now that you can put on your board and snap the shield into.