Assuming the report was official, then I would assume they knew what they were talking about.
Having said that, it can be quite difficult to judge how much oxygen is being used, especially if the requirement to top up oxygen to 1850 is required every time an aircraft returns to main base (which might only be 2 or 4 sectors). Engineers on the line certainly wouldn't know if there was high oxygen usage unless he/she worked 7 days a week and there were only a couple of aircraft in the fleet. Really, only large leaks are ever going to draw the attention of a line maintenance engineer (e.g. ones which generate low oxygen messages in flight after only one sector). Topping up the oxygen so frequently also makes it difficult for the people looking for abnormal trends in Technical Log book reports (Maintenance Control). I'd be surprised if anyone had a good idea of what's normal or not. Bottle temperature variations also have to be considered. If a pilot insisted that a bottle to be topped up to 1850psi in mid-winter in London (because his basic checklist said it must be this), you may see over 2000psi on an aircraft baking in the sun on the ground on the Gold Coast (in mid-summer). Hopefully the engineers could persuade the pilot that the 1850 value is based on 21C (70F) bottle temperature.
Did the report mention charter operations?
(EDIT: just read your latest messages. Questions to be asked: What are the top up requirements for Malaysian? Where was the A1 check carried out and by whom? The carrier or a third-party?