Thanks for the correction. You're right that quarantine does not require knowing whether people are actually infected. However, it's still about isolating specific people or things to protect the rest of the population and not about asking the whole population to change its behavior.
The Wikipedia article for cordon sanitaire [1] mentions quarantine as an alternative way to handle disease spread.
> Public health specialists have included cordon sanitaire along with quarantine and medical isolation as "nonpharmaceutical interventions" designed to prevent the transmission of microbial pathogens through social distancing.
