IBM executives typically don't have such a limited foresight nor would they typically assume their products would have such a very tiny market.
It's possible that he or whoever said that believed the computers would be limited to a niche market and that the calculators and tabulators would continue to have the largest part of computing market share. IBM had the largest part of the pre-electronic computer tabulator/calculators market and really those were computers themselves, just in a very limited way. The market for electronic computers would have been greatly limited if the best switch continued to be a vacuum tube. In that case, calculator/tabulators would have continued to rule the business world and most of government calculation too and he would have been right. And then, the transistor.
And then the IC. That IBM 'statement' was probably true for the time, market, technology, and customer base that existed at the time, which is what corporations are usually focused on, developing profitable products that customers will buy. Few envisioned at that time that individuals would some day be able to afford their own personal computers. Now if just those predictions about affordable practical flying cars had come through, I would be happier.