Even if they had 30% immunity, that still leaves the majority of the population exposed. I'm sure 30% would be very much preferable (if it's even true), but probably not good enough to allow things like concerts or maybe even sit down restaurants to reopen.
There are estimates that herd-immunity is achievable at 43%
"The disease-induced herd immunity level is 43% ... when immunity is induced by disease spreading, the proportion infected in groups with high contact rates is greater than in groups with low contact rates"
If you believe the disease is rampant in Sweden, it’ll be much higher now. If it’s not, then the hard lockdowns elsewhere were superfluous.