I'd say the biggest problem is that you decided to try and advance your quest at the expense of someone else, using their kill and thereby preventing them from using it. But the problem that's frustrating you is that when you use someone else's kill you see no animation, get no credit for planting a seed, but you do lose a seed. So if you've done this, you have to abandon the quest yet again and start over, or you will not have enough seeds to finish the quest.