One neat thing about UTF-8 is that all bytes that compose non-ASCII characters will have the high bit set. ASCII values range from 0-127, so no ASCII values will ever have the high bit set. Therefore, a byte that corresponds to an ASCII value is guaranteed to be the same character as the corresponding ASCII encoding.

No, the article states the method will correctly remove the mentioned whitespace characters even from UTF-8 text, because they are part of the 7 bit subset this method works on.