Bananas why did Russia go ahead on 2-1? Head to head?
The three team tiebreaker only considers H2H games between the 3 teams. Since all 3 teams were 1-1 against the other two, it goes to goal differential, which at that point was also all tied at 0. So then it goes to total goals scored in the games concerning the 3 teams, which Russia and Denmark were tied at 2 to Finland's 1. That makes Denmark 2nd, then Russia beat Finland H2H to get 3rd.
But Denmark scoring again gave them a +1 GD against the other two and Russia a -1 against the other two, making Finland's 0 good regardless of how much more Belgium scores (although it will hurt their GD in terms of the 4 best 3rd place finishers)