Try the below piece of code against a website that contains the form element. Check the result for ElementType returned and compare it against the Element Type Enumeration on the TestStudio API Docs.
The value returned is "OTHER" for element <form>.
Element element = Manager.ActiveBrowser.Find.ByExpression("name=paymentForm"); // Parent
if (element != null) {
Manager.Current.Log.WriteLine("\n Element Tag:= " + element.TagName + "\n Element Type:= " + element.ElementType);