Earlier quoted context omitted.
There wasn't an announced leaving date.
To get back to basics, the definition of resign is "voluntarily leave a job or other position." It doesn't mentioning leaving at the exact date and time you choose. She didn't want to work @ Google anymore, and she told them she didn't and she'd find a good time to leave with her boss. Google responded with "now is the best time to leave".
"Well sure, but if we use another definition about this legal situation that has no basis in the applicable law then Google wasn't lying" doesn't really hold a lot of water.
To be a resignation she needed to set the final date of employment. She did not, so it was not a resignation. Google knows this fact very well and therefore lied to the press about the circumstances.
You even use the phrase "Gebru firing" in your first post in this particular thread.