Absolutely makes sense. To function cognitively we build patterns that we apply to similar circumstances in future events, also called stereotypes. So if we see 10 brown people and find out they are all mexican, it is simply logical that the 11th one we see we will immediately jump to the conclusion they are mexican as well. Is this necessarily a terrible thing? Do people assume all white people they see in america are americans, when they could be germans or english or even spaniards? Or are people really supposed to walk up to every single person they ever see to verify their actual race and lineage before jumping to evil conclusions?
When referring to white folk nationality rarely is mentioned...it's usually "that white dude" which covers American, German, English, etc. To say otherwise is intellectually dishonest. I mean, if you used Hispanic you'd cover all nationalities. See.
Nah, it's definitely not a bad thing but culturally there's a hell of a difference...especially when it comes to Mexican folks and other central or South american people.
For instance, here in LA, there's quite a large population of Persian, Russian and Armenian folks. At times they are hard to tell apart but culturally they are wholly different.