I think what they are referring to here is the pin (about 5mm in diameter) that should drop down above the socket in your Tesla and locks the plug of the charge cable into your car while it charges. The charge cable plug has a rectangular hole in the top of it (about 6mm x 10mm) that the pin drops into while the car is charging.
The fact that this pin (latch) should lock the charging cable in makes me wonder about stories I have read of people having their car disconnected by others while at super charging stations in the USA.