Difference Between FS and FF Help

I changed the tasks and the wording so I hope I'm not violating any copyright.

I got this practice question wrong; I need help clarifying the difference between the two precedence relationships mentioned in the title.

Q: This is an apartment complex construction project. A task in your project involves installing floors in each building. The completion of the interior painting task is dependent on the floor installations in each corresponding building. What type of precedence relationship best describes the dependency?

A: FF

How is that the better answer than FS? Doesn't the flooring need to finish before the painting can start? The flooring finishing before the painting finishing seems like common sense. Obviously, the flooring needs to finish before the painting can even begin, therefore the painting will finish after the flooring finishes.

Does FS mean that the first task (the flooring install) must be completely finished in the entire building before the flooring can even start? So, in FF, the flooring can finish in one room so then the painting can begin in that room, while the flooring is still being installed in a different room. Therefore, task A has not completely finished, yet still needs to finish before the painting does e.g. the last room. Is that reasoning correct? Or have I missed the mark completely?