Wrong. When you are in the finishing straight you are supposed to stay in your lane unless overtaking someone. Bolshunov was trying to overtake Mäki, Mäki knew that and he moved over to block Bolshunov.According to Finnish media, the Russians have been sparing their best high-fluor glide waxes for Oberstdorf. In the skiathlon yesterday, they used the 4th best glide wax. That's why they have had issues with the skis in Lahti.
Moreover, Mäki did nothing wrong according to the rule book but the athletics stadium in Lahti doesn't really work for modern skiing.