I’m guessing that the matter wasn’t urgent enough, (such as an engine on fire), to require landing immediately. Therefore they burn off a few tons of fuel to have a more normal landing weight.
Possible, if it was an engine issue they have to be concerned about ETOPS.
It could be even less important than that.
Twin engine jets cannot fly more than 60 minutes from a suitable airport unless certain conditions are met. It is called Extended-range Twin-engine Operations Performance Standards (ETOPS).
Each airline, aircraft type, and individual flight gets an extension of that 60 minutes depending on conditions and fuel requirements. It can be extended up to 370 minutes, but is generally 180 to 207 minutes for Atlantic crossings.
There are equipment and weather requirements that must be met before entering an ETOPS segment. There could have been an issue with communications equipment redundancy, navigation equipment redundancy, fire or smoke detection redundancy, a back up aircraft system (fuel pump, APU, hydraulics, etc.) or maybe the flight would not meet the fuel requirements at some point during the ETOPS segment.
There was no emergency or abnormal situation (that’s a technical term) or the flight would not have diverted to CLT.
CLT may have had a spare aircraft, or facilities to fix the problem. The 777 can also dump fuel.
Everyone wants to give Boeing a black eye, but it sounds like the system worked as intended in this situation.
EC