Is this study an experiment or an observational study? How are you deciding?

In 1970 Linus Pauling, a well-known chemist and Nobel Prize winning scientist, published Vitamin C and the Common Cold (1970), creating a great deal of public and scientific interest. In short, Pauling argued that taking Vitamin C would reduce one’s risk of the common cold. This book almost single-handedly made Vitamin C one of the most widely used dietary supplements, a status it retains to this day (Nutritional Supplement Review, 2009). Subsequent to the publishing of his book, Pauling wrote a paper that appeared in the Proceedings of the National Academy of Sciences in 1971. In this paper he describes a study conducted by a physician in Basel, Switzerland, in the early 1960s. 

Here is an excerpt from the paper explaining the study design: 

The study was carried out in a ski resort with 279 skiers during two periods of 5–7 days. The conditions were such that the incidence of colds during these short periods was large enough (about 20%) to permit results with statistical significance to be obtained. The subjects were roughly of the same age and had similar nutrition during the period of study. The investigation was double-blind, with neither the participants nor the physicians having any knowledge about the distribution of the ascorbic-acid tablets (1000 mg) and the placebo tablets. The tablets were distributed every morning and taken by the subjects under observation, so that the possibility of interchange of tablets was eliminated. The subjects were examined daily for symptoms of colds and other infections. The records were largely on the basis of subjective symptoms, partially supported by objective observations (measurement of body temperature, inspection of the respiratory organs, auscultation of the lungs, and so on). Persons who showed cold symptoms on the first day were excluded from the investigation. 

After the completion of the investigation, a completely independent group of professional people was provided with the identification numbers for the ascorbic-acid tablets and placebo tablets, and this group performed the statistical evaluation of the observations. Although not stated explicitly in the paragraphs above, the participants were randomly assigned to take ascorbic-acid tablets or the placebo.