Someone else has already posted a good source for it. But I just wanted to add here that the Heritage Foundation is a conservative think tank particularly known for pushing "free-market economics" (read as: neoliberal policies of hyper-privatisation) so obviously it's on their best interest to label countries such as the nordic ones more capitalist than socialist.
And I mean, yeah, nordic countries for sure participate in the free-market... but Capitalism is defined by private ownership; so when you have such important portions of your economy be collectively, socially or communally owned (state, coops, labour unions) it's misleading to use such labels so lightly. These are mixed-economies, and I would even go as far as to say they're more socialist than capitalist.
Socialism does have a bad reputation though. So I don't blame for these countries to label themselves as "capitalist"; i mean, it's better for business.