OK so not RoundUp. I downloaded the Bayer Advanced Brush Killer Plus (active ingredient triclopyr as Rick mentioned) label and I can't see anywhere that it says "...the directions on the ivy roundup told me to pick all the tops off and then soak the ground with the roundup?" The nearest thing to that would be the cut stump treatment where you cut the top off a plant and treat the cut end of the stump. I think with Houttuynia it would be better to spray the plant intact as instructed on the label, and then give it time to work, because there isn't going to be much of a "stump". It says symptoms may take 1-6 weeks. This assumes that it works for Houttuynia.
