Excerpted from an interview with Rabbi Moshe Lichtman:
In any event, one of the sons living in Israel, Menachem, felt less antagonistic toward Medinat Yisrael and asked the Rebbe of Chabad what to do. The Rebbe replied that Rav Teichtal was a tzaddik, not a “Zionist” in the pejorative use of the term, and that the book was a legitimate Torah study about Eretz Yisrael.
So the son gave his permission on the condition that a letter from him would be included at the beginning of the book, explaining that his father was not a Zionist, but rather wrote the treatise out of his great love for the Holy Land.