I think it's just an (undocumented) artifact from the way set.itersection(*others) is implemented and therefore should apply to any other classes with methods that support a variable number of other objects.

To illustrate and prove my point, here's a custom class that supports this so-called "functional notation" via its own intersection() method.

Copyclass Class:
    def __init__(self, value=''):
        self.value = str(value)
        self.type = type(value)
        pass

    def __repr__(self):
        return f'Class({self.type(self.value)!r})'

    def intersection(self, *others):
        result = self
        for other in others:
            result &= other  # Perform via __and__() method.
        return result

    def __and__(self, other):
        return type(self)('|'.join((self.value, other.value)))


c1 = Class('foo')
c2 = Class('bar')
c3 = Class(42)
print(f'c1: {c1}')
print(f'c2: {c2}')
print(f'c3: {c3}')

# Both produce the same result.
print(c1 & c2 & c3)
print(Class.intersection(c1, c2, c3))

Output

c1: Class('foo')
c2: Class('bar')
c3: Class(42)
Class('foo|bar|42')
Class('foo|bar|42')

set.intersection() is an instance method. The instance is passed as the first argument implicitly.