Adam Smith wrote about free markets. Capitalism is something above and beyond a free market, first written about by Marx, who argued it was an inevitable consequence of free market and used that to criticize free markets.
You're arguing terminology over substance. Modern economists acknowledge that it was Smith who pretty solidly defined what we call "capitalism" as a socioeconomic structure. He didn't use the WORD "capitalism", but he defined everything we currently call free-market capitalism today.
Marx called it "captitalism". But we already knew what it was. Big fucking deal.