By Tzvi Machlin The Boston Celtics and Milwaukee Bucks are playing Game 1 of the Eastern Conference Semifinals right now. But one of the special guests in attendance apparently confused the heck out of two of the referees. At one point, the cameras panned to Grammy-nominated rapper Jack Harlow, who had a prime seat at TD Garden. But as referees Scott Foster and Ed Malloy looked up at the jumbotron, they couldn’t figure out what Harlow was famous for. “Who’s Jack Harlow?” “I don’t know. Who is he?” “Go ask him.” That exchange prompted the ABC commentary team to help Foster and Malloy out. They …