Wild. As long as no member of Homo sapiens planted the plant, the plant is wild by iNaturalist definitions as I understand them. You noted that you did not plant the plant, the plant “volunteered itself” into your yard. Whether a plant species was introduced to a location by people in the past is a botanic question and is not the defining characteristic of wild in iNaturalist, not as far as I understand iNaturalist’s wild. Sphagneticola trilobata was brought to the island I live on circa 1970. The plant rapidly went invasive and is now a self-sustaining population. The plants are all wild, no one since the early 1970s has intentionally planted Sphagneticola trilobata. See also the lengthy but worthy topic The category of “cultivated” is problematic for plants in urban landscapes and the help page examples - the improvement of which is the request made in this topic.