The investigators may simply observe a predefined set of individuals and collect the data from the observations, without influencing any factors involved. This is an “observational study”.
The investigator may design and perform their own experiments my controlling and manipulating factors of their choice and collect the resulting data. This is the “designed experiment”.
The investigators had no influence on whether an individual was left-handed or right-handed. The investigators could simply observe the individuals and form a conclusion from their observations.
Thus, the investigation is an observational study.