Mercantilism definitely is NOT a kind of capitalism. Adam Smith and other thinkers during the Scottish Enlightenment were specifically arguing against mercantilism. The Cron Laws in England were even successfully repealed by on of Smith's students.
In this case what we mean by capitalism loosely is a system of private property, free/open trade, market based pricing mechanisms, economic decisions being made by individual actors, etc.
So, private property was certainly there before Smith, as were individual economic decisions. But, there was a lot more price standardization and government planned trade.
So, is capitalism the same as a market economy? I feel like there are endless debates about capitalism and socialism but they are tribalized notions without clear definitions. Eg, are market regulations anticapitalist if they are government imposed or are they procapitalist if they support greater market health?
Not exactly, but that is a necessary condition. I think another necessary condition is that prices are set by the market and that the state isn't deeply involved in trade. Obviously there are grey areas, but it seems pretty clear that the export focused state trade policies of mercantilism were not capitalism.