Have new broadband fibre500- no cables outside- except the one through the wall covered with a grey coloured box
But neighbor has had an upgraded- now their is a black cable running from mine to the neighbour - is this a split fibre connection or something else ?
Splitters are not normally fitted on individual houses, they are usually in the underground chamber, but I guess it's possible.
Alternatively it could be 2 fibres are in the incoming cable, one spliced to your internal cable and the other to your neighbour.
If there was conduit already in place, it sounds as though theirs may have been blocked. The standard conduit sizes of 50mm and 90mm are more than enough to handle multiple cables.
*So long as it's not unsightly I wouldn't worry!