This story is not the mesora we have in Lubavitch of the meeting between the Gra and Baal HaTanya, (as I discussed earlier in this thread) but rather the version that Rav YB Soleveitchik had received in his family, being a descendant of the Gra.
Considering that this is a “family mesorah” one would expect it to be well know among the Brisk Rabbonim, Roshai Yeshiva, and their Talmidim.
Also, why are you making a personal attack against Rabbi Berger? Is it because he came out against certain elements in Lubavich? As you are well aware there are many Rabbonim who did (do) the same. Among them Gedolim whose reputation and scholarship is beyond reproach.