Presumably you mean that the 787 design specified these batteries
No I think he meant what he said which was that the design REQUIRED these batteries.
When the electrical system had been designed (requiring something like 1 MW of power!) the high energy density provided by use of Li-Ion technology was the only system which could provide such power at a reasonable size and weight.
A fait accompli in other words!
That is why this is not as simple a fix as some are trying to portray it. If the system can't be operated safely then either the batteries and charging system will need replacing for something a lot heavier and safer, or the electrical requirements of the model will need reducing. Either of those options is a headache and will take time. Ironically what they can take comfort from is that Airbus are running a similar system (albeit on a smaller scale) which seems to be stable.
As I said on the other thread, the best that Boeing can hope for is that this turns out to be a couple of dud cells in the two batteries which slipped passed quality control at Yuasa. ;-)