Kevin
The report states that it was believed that the performance of the tantalum capacitor was compromised by g forces in the crash. Tantalum capacitors are constructed to fine tolerances using extremely thin insulating layers between the plates. A heavy shock can crack one or more of the internal insulators and allow the capacitor to partially conduct electricity, causing heating of the component. If too much current leaks, the build up of heat will cause the tantalum capacitor to rupture, the exact failure mechanism observed in testing.
The report states that the tantalum capacitor was being operated outside of the range recommended by the manufacturer for that application, not that an incorrect value component was fitted. The design of the circuit board may have dictated that a smaller, less than ideally robust component was fitted due to space constraints, but there is no suggestion that the design was flawed and didn't work correctly. Tantalum capacitors are low voltage components anyway, so it may just have been a case of the capacitor operating at the upper edge of its design voltage with no headroom in case of faults or voltage spikes elsewhere in the circuit.
Electronic design is a series of compromises where the ideal component values are replaced by what is available on the market and what fits the circuit board. No different to compromises made in other areas of engineering. Capacitors generally are among the least accurate and most troublesome electronic components, so it might make more sense to fit overrated components in critical circuit areas. I suspect this is what the investigators meant by their comment.