All humans are genetically related.
Some Mexican Indians and Native American are more related though, and I'm not talking about just the Mexican Indians that lives near the border. The Uto-Aztecan languages are shared among many Indians from the US and Mesoamerica (like the Hopis from the States and Nahuas from Mesoamerica). The original Mexicas, that later formed the Aztec Empire, were probably genetically closer to Southwestern Native Americans than to Mayans because the languages are not related.
About the mannerism, genetics and behavior. I don't know how Native Americans act compared to Mexican Indian. I do know Mexican Indians or Mesoamericans tend to be quiet people, polite, and even passive, unless they have assimilated to the Mestizo culture then they can be very loud and annoying so I wouldn't say it's genetics but maybe similarities in environment, culture, and upbringing.