Planned economy as practiced by all vertically integrated monopolies may be the opposite of free market and the biggest attempt at communism was just that, but it's not the core idea of it.
Always good to cast yourself as unheard in your first sentence.
> where from comes the idea that communism is the opposite (or less of) capitalism
No one said they're opposite, but no one reasonably claims they're compatible. Communists, quite simply, want means of production to be collectively owned. There's a lot of debate among communists about what collective means, but no one reasonably claims that collective means "private ownership".
I dunno about the communists, but to me everybody owning shares of the company they work for sounds like collective ownership of the means of production. We could maybe argue about the threshold around which it becomes or stops being literal communism, because I don't this important KPI of ours in the article.
From literally every piece of communist theory/philosophy ever (okay, well, “opposite” is too strong, “radical response against and rejection of the basic premsies of", though...)
I mean, communism can be envisioned as sort of the maximum endpoint of a direction of change away from feudalism where capitalism is the first step, but...
The core idea is just what the article is advertising -- the person to see most benefit of their work is the one doing the work. Having enough shares of the company you are working for and high enough taxes to pay for nuking american fascists if needed is a) good approximation of it b) isn't just the opposite of what most of the supposedly capitalistic countries are doing, but is also a very good approximation of what they are supposedly doing.
This capitalism of yesterday was also a key part of protecting us from people being enrolled in totalitarian world views: people used to say "when trade doesn't cross borders, armies will". Now, with that monopoly/concentrated economy mindset, the thinking in the US has shifted to "we must cross borders to secure our interests".
Calling it communism is the kind of fucked up newspeak supporting less capitalism rather than more.