I think this happened because there's a place with the same name so the population from the other Gustavo A. Madero was used.
I found out because I made a quiz using geonames.org data to calculate cities that are larger than any city within 100 km. Do you know if there's a way (or it can be implemented) to calculate the distance to the closest larger city?
I also found some other mistakes (at least I think), should I write here on the forum or what? I tried editing Gustavo A. Madero population but it didn't let me.