Not surprising that there is a Litvishe Haavoroh and some crossover with the non-chassidish velt among the Bostoner Horowitzes. Its is somewhat of a family tradition, going back to Rav Pinchos the Hafloh and his brother Rav Shmuel Shmelke Mi’nikolsberg. Both were illuyim and inheritors of the Horowitz mantle of leadership and chochma from their ancestors, and both were Rabonim of their Kehilos and R’ Pinchos was an expert in Pilpul while R’Shmuel was also a Rosh Yeshiva. They were also among the earliest proponents/allies of chassidus, talmidim muvhokim of the Maggid Mimezeritch. This caused both of them, especially Rav Shmuel Shmelke, much trouble in their kehilos among those who were opposed to Chassidus.
The Bostoner dynasty are descended from Rav Shmuel Shmelke Horowitz. My family’s minhogim too are often chassidish, but have elements of a non-chassidish taam in them, as R’ Pinchos the Hafloh was my 7th great grandfather.