It is important to note that this map represents all hispanics, not just Mexican heritage folk. Although I expect that from basically Chicago and points west, the people are overwhelmingly of Mexican and Central American heritage, with a more diverse heritage, much more Cuban, Puerto Rican, Dominican, South American, in addition to Central American and Mexican, in the east of the US.
Yes, is it notable that the Carolinas, Georgia, Virginia, and Delaware all seem to have more of their countries with higher percentages of hispanics than southern states with actual longer history of Spanish rule like Oklahoma, Arkansas, Louisiana, Mississippi, and Alabama.
Yes, that's correct. Though it's worth noting that most Hispanics in the Southwestern US are likely Mexicans:
Mexican-plurality areas are in pink on this map, FWIW.