I appears that some entity with malevolent intent exploited a mempool-validation bug present in ABC at the exact time of the scheduled hard-fork. The intent of this attack is clear: cause maximum damage to BCH, and attempt to discredit all hard-forks by making it look like hard-forks cause chaos.
It's worth re-iterating: the exploit had nothing to do with the hard-fork. The attackers simply sat on an old vulnerability for months, waiting to exploit it at the same time as the hard-fork.
This exploit required expertise to discover. Whoever was behind this attack is either a security researcher themselves, or they've hired security researchers. This type of expertise isn't cheap.
Regardless of how well-funded this attack was, it has proven to be an abysmal failure. Within hours, miners have patched their nodes, and the network is operating normally again. In the end, BCH is now only stronger.