I think we've all seen great players go off in a 4th quarter before, it happens plenty of times each year. Thing is, it's almost always a LeBron, Wade, Kobe, Allen, etc.
For it to be a "scrub," a guy virtually unheard of, a backup to a star who mostly rides the pine, against a decent defensive team on the road in the playoffs... that's what makes it remarkable. And that wasn't just hot shooting, the guy killed the Spurs from everywhere. Nailing 3-pt bombs, drives to the hoop, even some nifty footwork Dream moves in the paint. No one could check him, he made Hill, Parker, Duncan, and Blair all look silly at times during the quarter.
Don't think I've ever seen anything quite like it. Spurs never could quite adjust to it because I think even they couldn't believe it.