Answer:
External validity
Explanation:
By controlling al the variables possible, and not generalizing some to global situations, or environments, he is correct to be concerned that his study could not have a general consensus outside the limits of his study, since it might not be replicable across other groups of people, situations, environment, stimuli, or times, this is called EXTERNAL VALIDITY, or the validity of the same study under influences of variables outside of the study's ranges.