Short vertical streaks in the dynamic spectrum of the Cassini/RPWS (Radio and Plasma Wave Science) receiver in the frequency range of a few MHz can be due to Jovian radio emissions or SEDs (Saturn electrostatic discharges). Although Jupiter is increasingly far from Cassini, the peaks of decametric Jovian arcs can still be detected a few dB above the galactic background, and in some cases they look very similar to the SEDs caused by lightning in Saturn's atmosphere. We show a method for discriminating between these two phenomena by using the ratio of the measured autocorrelations in case the receiver uses at least two antennas. We analyze the special event from July 22, 2003, which was interpreted as the first indication of SEDs at a time when the spacecraft was still at a distance of 1.08 AU from Saturn, and find that it originated from Jupiter.