I agree, you can't disconnect a measurement. He was trying to be cryptic and avoid saying the word 'neutral', perhaps so that he couldn't be accused of explicitly suggesting a dodgy method. I think he knows his job but what a lot of waffle! I could have said that with 75% less words.
As a few people have stated above, there are multiple techniques needed to cater for all possibilities with faults that cause intermittent or apparently random tripping. What I think is important to recognise is that 'RCD tripping' isn't a kind of fault by itself. The trips are just one symptom that shows up with many unrelated kinds of fault.
The faults most likely to cause intermittent trips can however be narrowed down into some clear categories:
1. Functional / normal leakage
a) No electrical fault but excess aggregate functional leakage for one RCD. E.g. large ring with low load but many appliances / computers etc with RFI filters. Identify by leakage measurements, identifying loads and usage patterns.
b) No fault on tripping circuit, aggregate leakage generally within limits but exaggerated at times, e.g. by voltage transients / spikes caused elsewhere e.g intermittent connection upstream or appliance with functional switching in neutral. Rare, difficult to find, might require logger.
2. Insulation fault
a) Intermittent hard fault from L or N to E, e.g. moving floorboards occasionally pinch cable against pipe. Identify by timing, usage patterns, insulation tests. Can include appliances with timed functions e.g defrost heater in fridge freezer.
b) Marginal continuous insulation fault L to E, e.g. water in external light. Identify by insulation tests, usually easy to find.
c) Hard continuous insulation fault N to E, e.g. neutral pierced by socket fixing screw. Identify by insulation tests. Can be misleading as trips can be triggered by load on other circuits, but faulted circuit will always be on RCD that trips.
3. RCD fault (rare, never seen it myself)
a) Internally faulty RCD. Identify by RCD tests, substitution.
b) RCD being affected by interference e.g. adjacent transmitter. Identify by inspection, testing, substitution, relocation.
4. External influences, e.g. cats, people maliciously interfering with RCD. Identify by psychoanalysis
From the diversity of fault types in that list, I think it's fairly clear that multiple tests and strategies might be needed to pin down the cause of tripping, not just lifting the final circuit neutrals from the bar one by one.