Not sure, what blog post you're talking about, but there's only really three things you can be doing wrong:

• Tons of cloning.
• Running your application from a debug build rather than release build.
• All the usual things one can be doing wrong in any programming language. Like, I imagine real-world raytracing is done on the GPU and uses highly optimized algorithms. I doubt a blog post would dive into those depths. And well, any kind of graphics programming is extremely slow, if you don't issue the exact right incantations that the GPU manufacturer optimized for.