Article states, that's because of "Combining pan-European firm-level IT data with our management practices survey, we find that the US IT related productivity

Article states, that's because of "Combining pan-European firm-level IT data with our management practices survey, we find that the US IT related productivity advantage is primarily due to its tougher "people management" practices." So it's not related to IT engineering skills but rather how the company handles those engineers. An US based company will handle EU based engineers like their own, thus nullifying your argument.