I think that she saved him. Earlier on in the film, there'd been mention of a legend of मत्स्य कन्याओं saving drowning men (but the legend was laughed at). I think it was true, and that they can also save people from dying द्वारा other means. I think that all मत्स्य कन्याओं are born female, so they find partners द्वारा turning human men into mermen.
