Every time a new model is released, everyone immediately tests it with a partridge riding a bicycle. Is it possible that this clip was pre-recorded, so whenever someone prompts for it, the system simply serves the pre-rendered video instead of generating it on the fly?
If you're using Gemini 3.8 Flash, I'd recommend sticking with version 3.7 for now. 3.8 seems to be a relatively immature release. I used it today to make some Vue frontend UI changes, and it couldn't even fix a small bug properly. As soon as I switched back to 3.7, everything worked normally again.