Men who were draft eligible during the Vietnam War knew in considerable detail what various categories meant. When George W. Bush joined the reserves, reserve units were simply not being used in Vietnam. This may have been because the active duty military was expanded to the degree that it wasn't necessary. But an officer in the reserves had zero chance of seeing duty in Vietnam. So, yes, he was a veteran, but no, he wasn't subject to duty in Vietnam, unless the reserves were called up, which they weren't. The methods of circumventing Vietnam duty were expansive, and depended partly on local draft boards. People avoided military service through service the Peach Corps, by having a parent buy them land to be be farmed thus (in some places) gaining a farmer's deferment. People in medical school, law school, and in some cases in some places, seminary, could be deferred. The catalog of "outs" is much larger than that, but those are examples. Later it was lottery numbers, and eventually they just ended the draft, although men in the U.S. must still register, as you know.