That looks like a seedling to me. I allowed a hardy hibiscus in my own garden to go to seed and then I protected the young plant. After three years I now have a new shrub about 3 feet tall. Gardening is a great adventure so go ahead and let the seedling grow and see what you get. Sometimes the new plant does not look like the parent but then you could get a new cross that is even better than the parent plant. That is what makes gardening so fun. Keep growing, Marianne Binetti