When you say they turned back before the "CP", was this the CPE ("Critical Point ETOPs"), or was it the ETP (equi-time point)?
They are not the same thing.
An A330 CP (ETOPs) is calculated on simultaneous engine failure and depressurisation, which is the most fuel critical scenario. If you don't have both, the CP (ETOPs) becomes rather meaningless, not to mention that its calculation is a preflight requirement but not an inflight requirement. A cruise depressurised at 10,000ft with an engine out is not equal to a cruise at engine out cruise ceiling.
Now, they did not divert to the Marshall Islands (Majuro) but proceeded to to HNL:
For an A330 (at least in QF), Majuro is classed as a "Category C Airport". That is, it is only to be used as an "adequate" airport for the purposes of ETOPs planning. It is not an approved "Main" and it is not an approved "Alternate". In QF rules and regulations at least, it is stated crystal clearly that there is no requirement to land at the nearest adequate (i.e., a cat C) airport in the event of a critical systems failure.
The crew (at least if they were QF) were completely and totally within their rights to continue to Honolulu - and probably quite sensibly too. I've flown a lot into the remote Pacific airports and to force me to do it in an A330 the situation would want to be pretty grim.
**yes I'm qualified on the A330 in QF.