The firewood is an indicator of the immense privilege of whoever's inside the house. Kolya understands immediately what's going on, while it will take Lev a few minutes to catch up and realize that the girls are being kept as sex slaves. Notice too that Kolya is angry at women being treated this way, providing clearer evidence that his perception of sex, while often manipulative and arrogant, never approaches the inhumanity of a situation like this. He often describes women as “conquests,” but clearly still sees them as human beings with dignity and value.