Erm, if you take "content creation" to mean full, playable games then you're right. But...
I'm pretty sure Valve is referring to content at every level, from hats to in-game items to custom levels to mods.
His point stands, however, and you only have to look at the quality of many of the Steam Workshop addons produced by hobbyists. Yes, this includes plenty of high poly models and much more, easily comparable to anything produced professionally.
But what I was saying is that these guys are making single models of very high quality, not filling out an entire GTA V5. And especially not coding, acting, mocapping, producing, marketing etc a game. They're not even building somthing like bastion with a small team. They are many orders of magnitude between doing one model that sells well and building a full game. Especially one that does well.