One way of looking at a union type is "this variable can have different types at different times." Another is "this variable has a single type - the union type

One way of looking at a union type is "this variable can have different types at different times." Another is "this variable has a single type - the union type." Especially if actions are restricted to those valid on all parts of the union, I'd say it is correct to consider that to still be static typing.