I think his point is that the choice of language at google isn't exactly a managerial or strategic decision. They just happen to have a lot of java devs (probably at senior positions now, since they were hired a long time ago).Even if they have gone out, if most of your stuff is made in a language, it would be really difficult for new comers to shift that paradigm to some other language.

The part about C++ was to describe a similar scene. When they had mostly C++ devs, their language of choice was C++. and now they have mostly java devs, so java it is!