Hola Cate

For the lessons that are specific for Latin American Spanish, with a specific way to say something that is different to the European Spanish, we take into account what is wider across Latin American countries, giving special consideration to Mexico. For example, if there is something that is just used in Uruguay and nowhere else, we wouldn't include it in our content. 

This specific lesson about the use of the perfect tense and the preterite tense in Latin America is compiling the most generic usage of these two tenses, trying to differentiate specific context to use one or the other. This doesn't mean that a person in a part of Mexico could use it a bit differently to what we're saying in the lesson, because there may be also some regionalisms or a custom in a place to use these tenses in a different way - however, the scenarios explained in the lesson are a summary of what is mostly used in Latin America. 

I hope this clarified it.

Saludos cordiales