Earthing a 2-gang wall socket?

Hi all,

Have just changed a 2-gang 13A wall socket in the lounge (downstairs ring main).

All very straightforward, but I did notice that the earth (2 wires, because it's on a ring circuit) is connected to a terminal on the junction box, rather than to the earth terminal on the fitting.

I am assuming this is just another means of achieving the same thing, but I would be grateful for your confirmation.

Many thanks.