ECS is closer to the second way that was described. Data is represented as arrays of structs (referred to as components), similar to what was described. Systems can mutate or read these structs.
A physics system might change the position components while a decoupled rendering system might read that position components and the rendering details components to add draw commands.
A physics system might change the position components while a decoupled rendering system might read that position components and the rendering details components to add draw commands.