Perhaps he really was a very talented developer but your coding exercise was too stressful for him. Shame you missed out on hiring him.
This is not a story to show why we should do coding exercises. It is a story to show why they sometimes don't test the right thing.
1. He knows how to do extremely specialized things in an existing environment, but can't do things outside of that environment.
2. He was presenting work that he had only a partial hand in creating.
3. He is amazing at e.g. C++, but cannot learn even rudimentary new things in Javascript.
...
Some of these stories make him a terrible programmer. Some of them make him an OK programmer for other positions, but weren't relevant for us. None of the stories make him a particularly great programmer.
"Perhaps he really was a very talented developer but your coding exercise was too stressful for him"
Yes, it's possible. A lot of things are possible. But I'm sorry - if someone can't copy-paste a 3 line program from the internet and get it to work, in their own field, for 2 hours, then... I don't know how I could ever design a test on which they won't fail. Including the actual job.
Ya.
As far as graphics, the only time I was ever fooled was by a front end guy in 2005. He brought really nice looking color printouts of his front ends; beautiful stuff. I was really wowed by it; so much I didn't ask him basic programming problems or follow up questions about his prior work, and that was my fault. I allowed myself to be fooled.
His biggest issue was he was lazy. He had grown accustomed to government contracts where you do a lot of prototyping, but nothing ever went live (at least the contracts he had). We had a very aggressive 3 year schedule to build a sophisticated product and he just couldn't or wouldn't keep up. I had to double my workload and he ended up only doing about 5% when he should have done a third and he required a lot of prodding and hand holding. We still managed to ship on time though, but it was really hard on the other 2 people on the team for 3 years.
I'll never make that mistake again.
I had a candidate for a 3d graphics job, who showed me incredibly impressive things he'd programmed like very realistic water simulations, etc. He talked us through them, was incredibly articulate and clearly knew his stuff.
He completely bombed the coding exercise. It was something like: given 2 hours alone at a computer, with a threejs scene already setup, make it display a few cubes at different heights, colors, etc. Full access to internet, google, etc.
He couldn't get one cube to show up. That's maybe a two line piece of code when given the entire environment already set up, and you can find it by googling Threejs tutorial and copying like the first example.