why VARIADIC functions executed on array input?

CREATE FUNCTION foo (VARIADIC anyarray) RETURNS void AS $$
DECLARE
BEGIN
END
$$ LANGUAGE plpgsql;
SELECT foo (ARRAY[1]);

I would expect an error: Like:
ERROR: function f3oo(integer[]) does not exist

But I get this error:
ERROR: could not find array type for data type integer[]

Why VARIADIC functions are found on array input? In my opinion it
makes no sense and the disadvantage is that overloading with a
function like: CREATE OR REPLACE FUNCTION foo (anyarray) doesn't
work.

Greetings Tjibbe

see example in: http://sqlfiddle.com/#!15/300e8/1

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