To me, it was primarily Cascade-esque white grapefruit. I got a faint, weird savory note from it as well - not quite garlic/onion, but maybe approaching it just a tad. Honestly, I wasn't that impressed when I tried it. It wasn't bad, but there was nothing that stood out as all that interesting, either. But weather/growing/harvest conditions all make a difference in hop character, so hopefully your Riwaka is better than the ones I had.
All that said, Riwaka + Galaxy definitely has potential for the citrus/passionfruit bomb you're shooting for.