Starting with the ingredients list, the American recipe is already a lot more specific, indicating the amount of olive oil to be used and that the onion should be yellow and chopped. The Spanish recipe just says 'aceite' and 'cebolla', with no reference to what kind or how it should be prepared for cooking. In the instructional paragraph for how to make the tortilla, the American recipe is still a lot more specific. It includes instructions to put the potatoes in 'carefully' and tells the cook what to do if the accidentally stick together. However, the Spanish recipe is a lot more vague in its directions, telling the reader to remove the pan from the heat 'de vez en cuando', or once in a while. The American recipe also gives more explicit instructions for how to get the tortilla from the pan onto the serving platter, while the Spanish recipe assumers the reader will know how to do that.
I think a lot of the differences between these two recipes make sense based on the cultures they come from. In Spain, the attitude towards most things, cooking included, is very laid-back, so there is no need for troubleshooting advice in the recipe. In American cooking culture, people making the dish are more likely busier and will have less patience to try and figure out when the eggs are cooked enough or start over if something goes wrong. Although these two recipes have similar ingredients and similar results, the way the methods are portrayed to the audience can tell us a lot about the culture they come from.