I'll dig around and see if I can find the source where I read this, but otherwise it looks like I was wrong. My bad.

To back that chart up, photosynthesis generally works at around 5% efficiency.

Perhaps he means if you're using solar cells followed by Fisher-Tropsch to make actual fuel.

I'm pretty sure plants beat that.

But the base efficiency of plants is horrible : 2% is relatively high in plant species (solar energy input -> produced plant matter output). The most efficient plants in the world are close to 4.5% efficient.