Good question. I followed the citation in wikipedia and it points to this article: https://languagelog.ldc.upenn.edu/nll/?p=1997 https://languagelog.ldc.upen

Good question. I followed the citation in wikipedia and it points to this article: https://languagelog.ldc.upenn.edu/nll/?p=1997 https://languagelog.ldc.upenn.edu/nll/?p=1997 In the comment thread there, people are discussing the question you raise. Essentially, it's the inclusion of the word "they" which makes the sentence incorrect. If the word "they" was removed it would be valid and would mean what you read it as.