The league doesn't build stadiums. The individual teams build stadiums, or, more correctly, cajole their home cities/states to build stadiums for them.
The league must have had a program where the league loaned money to teams in order to allow the teams to contribute money towards the building of that team's stadium. That means that the government in the state where the team and stadium are would have had to have contributed less money to the building of the stadium.
The league must have allowed certain teams to not pay back all or part of these loans.
How exactly that changes the tax liability of the league I can not say. I will trust the Times on that part.
Student or Learner