The study depicted is an experiment.
An experimental study is a scientific approach in which a researcher articially generates a controlled environment, in which he/she manipulates certain variables and waits to observe the results of those manipulations. For example, in the case presented the researcher is offering a choice to the participants.
If it had been an observational study, the reseracher should have waited until such situation appeared naturally in the lives of the participants in order to observe its result.
