Close up only because he used a handgun. That's the only difference and Zodiac and the Son of Sam both taunted police by sending them letters. Son of Sam was even more brazen than this sniper - he walked right up to the car and shot them. Sniper killers all have their own MO but they still fall into the Serial category.
A sniper by definition shoots from a distance, unseen. You cannot be a handgun sniper. Son of Sam was a serial killer, but not a sniper.
Zodiac was a sniper, but it was racially motivated, not random.
Charles Whitman was a sniper, but he shot from one location and did move methodically from one location to another.