Does the 969973-3 SMD receptacle need mounting holes?
It looks to me like it's possible to poke a wire or mating connector all the way through the board, or insert a wire or mating connector from the back of the board, if those holes are present. This allows easy board stacking without needing the full height of the connector between the boards.

In fact, this seems to be corroborated by these sections of the linked drawing:







Notice that note 5, "Only with the bottom entry" is specifically marked on the holes you're asking about, and that note 3 states that top and bottom entry are both options for this device.