It's linked to why the RCD tripped. The N conductor is connected to other N conductors inside the consumer unit.
It is possible (should any of a number of things happen upstream, inside or outside your house or with the supply) for the current path of other circuits in your house to go via the socket circuits N wire, via you, to earth.
This reason was why I said "or better use the main switch".
@Risteard is spot on that really it should be the only approach in your situation.
You might get away with it 99.9% of the time, but if the supply N happens to break at the wrong moment, it's curtains time!
(This is one of a number of reasons why new consumer units that I fit have double pole isolation on each circuit and separate RCD protection for each circuit. They are much easier to do maintenance on!)
There are other reasons too related to the average experience of DIY people doing this, that would not necessarily apply in your case.