This is just one study. The author admits herself that there has been a dearth of studies examining the effects of political correctness on group behaviour.
Also, this study only examines political correctness in the workplace. That is only one aspect of political correctness. Most critics of political correctness do not argue that PC culture is detrimental to the workplace, they argue that is detrimental to free speech and the marketplace of ideas. This study does not disprove that PC culture has a negative impact on freedom of speech in the public sphere, only that in the very specific context of a meeting in a professional environment it MAY contribute to creativity and innovation.