If you look at one of my first post in this thread, I address this, albeit obliquely: According to the (EU) Reg, it applies to passengers on EU-bound flights from third countries on EU carriers "unless they received benefits or compensation and were given assistance in that third country." (that is the wording of the Reg)

Now there is (as in so many other aspect of the Reg) some ambiguity as to what exactly this means (for instance, where the benefits received are derisory or substantially below the EU levels, for instance), an ambiguity which, if the jurisprudence of the ECJ is anything to go by, is likely to be resolved to the pax's advantage. Given that BA does not appear to have given the pax any benefit in the third country in this case, they would, imo, be ill-placed to argue that compensation is not due on this ground.

As to compo under the US rules, it would be $800 in this case, which is only marginally lower than the €600 provided for in the EU Reg. For long-haul flights, the EU Reg also uses a 4-hour-later-arrival cut-off point to determine the point at which compensation can be reduced by 50% (viz. €300 vs $400 under US rules, so again quite comparable). The main difference is if the arrival time is within the hour of that originally scheduled, where you would still be entitled to €300 under EU rules whereas you would be entitled to nothing under US rules. AFAIK, there is also the difference that there is a reporting requirement (to the FAA, IIRC) under US rules for IDBs whereas no such requirement exists under EU rules following heavy lobbying against it by EU airlines.

Re KIN, this is somewhat OT but I am curious : is it the case that US rules only apply to outbound flights from the US and not to flight TO the US even on US carriers?