This is inaccurate. He made the initial discovery while helping someone with an earlier experiment, and noted that the chief experimenter was disappointed in the experimental subjects (which interfered with the intended progress of the study). But for Seligman the main point was that the dogs had learned to be helpless. Later on, he designed a simple experiment to prove this (serendipitous?) point.
Many accounts get this wrong.
Also, Seligman has his opponents and detractors. The connection between pessimism and depression is not well known, let alone widely accepted. His comments about self-esteem are especially unwelcome in the education community, as his critique amounts to a charge of pseudoscience against self-esteem advocates.
- Seligman says self-esteem is a byproduct of competence, and that attempts to increase competence by buoying self-esteem are not just ineffective but even counterproductive. (Others have noted that juvenile delinquents and dropouts have higher-that-average self-esteem.)