Something went wrong with this Falcon 9 flight. Assuming little has changed in its design over previous flights then that something could have happened on any previous flight and SpaceX were just lucky it didn't happen on an earlier flight.
The goalpost-shifting criteria of "how many successful launches do you achieve before the first bad one happens" is not something the insurers will look on with equanimity. What they want to see is a long unbroken string of successful launches like, say, the Ariane V which had its last failure back in 2002 and which has launched sixty-four times since then with every mission an unqualified success (no OrbComm-style failure-to-achieve-correct-orbit in that sequence BTW).
As for the Japanese HII failure, a strap-on motor on an HII-A failed to separate after burnout and it was aborted by the range safety officer. It was flight number 6 of that design.
The larger HII-B has four successes for four attempts to its credit, all cargo flights to the ISS. Hmmm, just ran some numbers -- the four Japanese HII-B resupply missions have delivered 19.8 tonnes of supplies, spare parts etc. The six successful SpaceX CRS missions have delivered 9.7 tonnes of cargo in total, slightly less than half that amount.