If you are not a student at the school or booster or employee, in this case NU, it doesnt matter. The NCAA can/could do nothing about it. Now, being a student at a school, that could be different as you read in the article. Regardless though, I think the point people were trying to make is to show the support of the fan base.
In any case, its more fun to talk about the the alternative, which is not talking about college football because the season is over and its totally boring now!
The NCAA won't do anything to an individual, whether associated with the university or not. What the NCAA can do is sanction the university. So even if you are not a student, booster, or employee, the NCAA can still go after the school you are supporting. To my knowledge, the NCAA has never actually done this, but it is possible. The NCAA is a private organization, not a government agency, so they can make whatever rules they want. However, as the article above points out, the NCAA could end up in some sticky legal problems if they tried enforcing the rule.