How did the community at large explain Sirius's being a Gryffindor while he was still believed to be a faithful follower of Voldemort?

In Philosopher's Stone, Hagrid says that "there's not a single witch or wizard who went bad who wasn't in Slytherin," and yet Sirius Black, a Gryffindor, was still considered to be one of the most dangerous and evil wizards alive at that time. While Hagrid's statement turns out to be true, he didn't know that at the time. How did the community at large explain Sirius's being a Gryffindor while he was still believed to be a faithful follower of Voldemort? Might they think the sorting hat makes mistakes?