I can imagine that the baggage systems at LHR are automated enough that human involvement (at this end) doesn't have much to do with it, unless those actually unloading the containers want to make their life more difficult by deliberately holding back bags from entering the baggage system.

It seems most likely that the bags were loaded at NRT in a way that the container containing the priority baggage from the club cabin was put in first and therefore was the last one to come out.