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.
Semantics.
Yes of course aircraft designers always want to save weight and space, and Li-Ion tops the list on those criteria, but that's not the same as saying that the 787 could not have been built without that particular battery technology.
Of course hindsight is a wonderful thing ...