Obviously, there's something compelling that resonated with everyone who shared it. So, as a brand manager I wonder what I should share that actually resonates with my audience. What if it's something that another brand has created? Is that considered "promotion?" Is that considered "wrong?"
Well, as it turns out, it's just considered "real." Real people share things that they think their friends will like. Real people share things they think are important or worth reading. That's why brands that share other brands posts, are actually providing value to their social sites.
If you're a marketer who believes sharing content that doesn't link back to your site is not accomplishing your goals, then you need to evaluate your goals. By sharing other content, you're providing something for your audience that makes you much more like their friends and a lot less like a pushy brand.
When you find that great piece of work in the future, don't be afraid to share it!