I have always, my entire life, greeted people with a "howdy." Not an in-your-face "howdy" like aggy does, but "howdy" all the same. It is NOT an aggy thing, it is an old school Texas thing. In the 1970s in Llano, San Angelo, Marfa, Harlingen, and a half dozen other places where my family was scattered about, I'd visit relatives with zero connection to the li'l farming school in the armpit of Texas, and they'd all say "howdy" as a greeting.
I get the feeling the term went out of favor, actually, as soon as the media presence for aggy increased enough that people started associating it with Texas A&M. They are so obnoxious that they ruin everything they touch, including a good old fashioned Texas greeting.