And that is the answer to the mystery. The Russian mansion is VERY similar to the Russian Pavilion on the "Street of Nations" featured in the 1878 Paris International Exposition. At the link above, <
Paris 1878 Exposition: History, Images, Interpretation — Ideas> I found this image of that pavilion. The central part, leaving off the two wings looks like the little matchbox model, including the dramatic entry with the crested front, the roof forms, and the two flanking towers. Wonder how many of the other little models are of the 1878 Expo Pavilions?