He was a pioneering Islamologist and his work still has value as a synthesis of Islamic sources; hence his inclusion to the list.
well you may call him
"pioneering CHRISTIAN Islamologist".. whatever Islamologist means., True he took whatever written in hadith & sunnah and put his Christian glasses to write that book but the fact he says statements like these means
"Muhammad had fallen under the influence of Satanic inspiration"
"First: Polygamy, Divorce, and Slavery strike at the root of public morals, poison domestic life, and disorganise society; while the Veil removes the female sex from its just position and influence in the world. Second: freedom of thought and private judgment are crushed and annihilated. Toleration is unknown, and the possibility of free and liberal institutions foreclosed. Third: a barrier has been interposed against the reception of Christianity."
in his book, he was just analyzing so called Islamic historical Muhammad from what was written in hadith and Sunnah by so called Islamic intellectuals of earlier times. Suppose you remove those two sources and take Muhammad character just from Quran , then we will have entirely different story on Muhammad.
Any way this subject is quite complex..