According to the tagged union Wikipedia you referenced, a disjoint union is also considered a tagged union. Whether or not that's actually a correct description within the vernacular of computer science, I don't know.
"In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, disjoint union, sum type or coproduct, ..."
"In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, disjoint union, sum type or coproduct, ..."