That discussion was in an email conversation with, among others, Finland, where they stated that they've had the same thoughts about herd immunity. All countries have discussed herd immunity at some point.

However, herd immunity was never the goal, as you can read from the email exchanges in the original source the article links to. It was merely a discussion about a possible side effect of the actual goals, which was to prevent a collapse of the Swedish healthcare system, and to prevent side effects that lockdowns have (because they're not a silver bullet either).

Now, if they were successful is another question. I'm a Swede and I do not agree with our strategy.