"I'm leaving to work on my own thing, but don't have an idea yet."
My mind translates that into:
"I have an extremely clear idea of what I want to do, I also am extremely aware that any ideas that could possibly be thought of on company time may be claimed as the intellectual property of my employer."
This may or may not be the case of Gabor and Google as I can't speak to their intellectual property arrangements, but there is nothing quite like a very public statement that you are intellectual property unencumbered to start things off.