That hard fork was rolled out over a period of two months, with warning (whilst older clients were sent messages to upgrade) and smaller splits are part of the

That hard fork was rolled out over a period of two months, with warning (whilst older clients were sent messages to upgrade) and smaller splits are part of the protocol and happen quite regularly. as expected (like when two miners hit the same block within seconds and they wait for the network to recognise the block). That is the justification Satoshi Naakamoto gave in the original paper for waiting for 6 blocks for a full confirmation.