electrons actually loop around in a closed DC circuit in the speed of light
On average, electrons “move forward” much much slower than that:
https://en.wikipedia.org/wiki/Drift_velocity
But even the whole “electrical signal” is slower than the speed of light:
https://en.wikipedia.org/wiki/Velocity_factor#Typical_velocity_factors



I think google hides an additional mark in their own edits so the tool can perform an actual check in this case.
They would not detect any AI edit from other providers.
There are tools to remove these hidden “signatures” E.g. https://github.com/wiltodelta/remove-ai-watermarks
I’m not commenting on the ethics.