Nope, nope, and nope.
Stardew Valley has a notable indie publisher. There was marketing on various internet communities (reddit, 4chan, etc) leading up to the months of release. There it can pass off as organic word of mouth. Terraria was marketed months before release. As for Minecraft, Notch himself was throwing his game around a load before it got released and using anonymity to drive interest--it was the most organic of the 3.
Other notable indie games like Hotline Miami and Super Meat Boy also had especially significant marketing efforts behind them. And let's not forget Fez.
Most indie breakout hits aren't miracle successes. The just have very clever and modern marketing methods. They're not wasting money on magazine ads and gaming news sites banners like AAA studios do.
Bullshit claim. They did really clever marketing where they provided the beta release beforehand to few prominent twitch streamers, and in my knowledge also did all kinds of other pre-release hype, community building etc. I'm pretty sure also the other titles invested quite a lot of time, smarts and money towards marketing.
These 3 games did a lot of marketing. It was just not the millionaire kind of marketing that EA does.
... ish.
You can certainly think of the prolonged free alpha (and beta?) as marketing
Also he made a highly viral video of him building a minecart rollercoaster during his paid (but cheaper, I believe it was $13, and he was telling people that was half the price that it would be on official release) beta which he got Kotaku and Penny Arcade to share with their massive audience and suddenly he was a millionaire pretty much overnight.
I personally saw the minecart rollercoaster video while browsing Kotaku and that's how I discovered the game.
Notch absolutely marketed and knew how to market his game. He may have not had an advertising budget, but he made the right type of content and the right type of advertising, then shared it with the right types of promotional avenues to reach his target audience to get enough of a start that word-of-mouth advertising could pretty much take over. And that's all marketing really is.
And since then (especially since Microsoft bought Minecraft) you better believe that game has had lots of money dumped into its marketing.
It's just that most things aren't as sexy as a build-your-own-minecart-rollercoaster-brick-by-brick-and-ride-it-in-first-person and therefore require a lot of money to get it in front of enough people.
I've experienced many marketing failures for video games as well (both games I made myself and games I worked on for other companies), I should be an expert on it by now. Guess that means I should make a new game and apply all those lessons I learned :P.
This seems very logical but indie games really do seem to defy this general rule. Pretty much every single popular indie game out there is really, really good in it's own specific way, and most of them had almost no marketing budget (when they first came out anyway).
Minecraft had no marketing. Terraria had no marketing. Stardew Valley had no marketing. These games spread through word of mouth and quality is the main criteria that causes people to talk about a game.