That article states that globally Soccer makes more money than the NFL. Just adding up the 5 Soccer leagues listed in the top 10 there, they total more than the NFL. And there are a bunch of soccer leagues globally that aren't in the top 10. So while the NFL does have a commanding lead as the largest sports league globally, American Football is indeed behind Soccer globally as a sport.

Another way of thinking about why that is is that the NFL is effectively a monopoly. They are the only game in town for a sport which is only popular in one country (the USA). Soccer is, globally, a much more popular sport than American Football, but it's not controlled by a single league (FIFA is a governing body (a terribly corrupt one, but that's a separate conversation), not a league).

If you look at it per-capita, the NFL also seems a bit less impressive, and their revenue might be more a result of the fact that the USA is both rich and fairly large than any strong indicator of global popularity. Taking population estimates from Wikipedia, the NFL made roughly $39.76/person in the USA, and the Premier League made roughly $80.30/person in the UK. (And that methodology is arguably a bit generous to the the NFL, since the Premier League is technically only in England, but I'm including the rest of the UK since they also do watch a lot of Soccer AFAIK.)

To me the enormous revenues of the NFL is a stronger indicator of why monopolies are harmful than of any special virtues of the NFL or American Football.