He was a Confucian, with a rather dark bent. He was pessimistic about human nature.
It looks like this quote is legit, or at least widely attributed to him, but "heaven" in ancient Chinese thought is not what most Westerners tend to think of it as. It's "that which makes things as they are", so at best, an impersonal Force type of thing.
Even adjusting for that, though, it does sound very secular humanist / atheistic, I agree.