It is.
The grouping is done by checking for equality.
And quoting Raymond about all_equal (or its old recipe version, not sure):
Which is perfectly fine and normal. Do you also dislike all’s equivalent code
def all(iterable):
for element in iterable:
if not element:
return False
return True
because it’s supposed to check whether all elements are true, but instead checks whether they’re "not* true and doesn’t even check all elements, instead using the first not true element to “prove by contradiction that all the elements are not true”?