Thinking about it, you're right. The GK Speakon is just a four-pin speakon, so the lows to go to pins 2 and 4, and highs go to 1 and 3. Plugging that into a non-GK cab would just leave an open load on the high range amp, which wouldn't damage anything.
OTOH, maybe the cable said "bridge" on it somewhere?
