Using a "sled" might be unusual behaviour, but sliding down rooves certainly isn't. The sound of crows screeching their way down a metal roof is my least favourite way of being woken up - and it happens frequently. It doesn't snow here, so I guess their feet don't get cold enough to bother with a sled.
Yes that crow is cool, but is it non-black? I think I actually saw traces of grey in its plumage. Which would mean that Hempel was wrong.
But it isn't a raven, so Hempel could still be right. It's a crow. They are both corvids but they are not the same.
What we call a magpie in NZ is actually a small black and white crow.
My wife and I were watching a doco on the crows that live in Japanese cities, it was really interesting. One of the things it brought up was that city crows are often able to scrounge food quite easily, so they don't have to spend all day looking for something to eat. And when a smart bird like a crow gets spare time, they find creative things to do.