Idk, but watch this live demo: https://youtube.com/watch?v=69vx8ozQv-s He couldn't do it.
There could have been multiple versions of Gemini active at any given time. Or, A/B testing, or somehow they faked it to help Google out. Or maybe they fixed it already, less than 24 hours after hitting the press. But the current fix is to not do images at all.