Tegnell was wrong.
He predicted that the virus was circulating many times more widely than people thought (20-25%) -- and posited much of his strategy on that.
In reality that appears to be closer to 7%.
He was also particularly wrong in attacking other countries - and the underlying Imperial College study that influenced them - for locking down in the way they did.
18.1m people came in and out of the UK between January and March in the UK -- nearly twice the entire population of Sweden. What was optimal for Sweden would never have been optimal for others.