I am so relieved that someone had the answer, albeit slightly ashamed that I couldn't find it online.
As for where I got the answers, my favorite veg-head Astronomer, who earned his stripes eating Durian and all sorts of what must be weird food on his trip to HK, was the first one to guess. And I really should have thought to call Umami, who is a virtual treasure trove of answers regarding food. I have yet to name something she has not tried.
So, how did it taste? Well... I opened one of the passion fruits to do a true comparison. It is definitely sweeter and much more mild with a subtler taste than the passion fruit. The seeds were much softer and tasted vaguely of sunflower seeds, which makes the overall taste a little more bland. The passion fruit on the other hand was tart with hard little seeds and a more beautiful fragrance.
I'm very grateful to receive this p'tit cadeau and to the friends who helped me identify it.