Where I come from, when we speak of “puritans”, we refer to people who believe that sexual abstinence before marriage is an absolute AND who insists on forcing that view on everyone else around them.
While the Swedish stereotype may be of a wildly promiscous bunch of heathens, it’s not very accurate. A girl who’s slept around a lot is still considered a “slut” and not very desirable and a guy who’s been with many girls is still considered “untrustworthy”. While we may be more “liberal” towards sex, we’re still predominantly monogoamous and sex occurs mostly within commited relationships. While it’s socially accepted that 16-17 year olds engage in sex, it’s also encouraged that it should happen within a relationship and that parents should be aware of and approve of it.
To expand on my original point, we tend to leave to issue of sexual morals up to the families and less to state-controlled indotrination. Sure, the schools gives us some guidance on how to use contraceptives and the meanings and risks with STDs and pregnancy. The teaching that abstinence is “unhealthy”, however, is not anything I’ve encountered, either by myself or heard from any of my siblings or friends of mine that are parents. And we dont shun people who made a choice to wait with sex. A 25-year old virgin by choice is a lot more accepted than a 17-year old who’s had 5 different partners already.
When we look at the US, we see a very polarized debate, with absolutists on both ends beeing very vocal. This is probably what’s spawned the general view that the US is “puritanical”, as you put it.