As far as I can see, calling Tegnell a scientist is incorrect. He may have a Ph.D but does decisively not behave scientifically. Instead he should should be called a bureaucrat, which much better describes his behavior.
The catastrophe that is swedish covid-19 strategy, probably started as something like this: http://www.openias.org/swedens-covid19-strategy
They believed Covid-19 was much more infectious and much fewer people were seriously affected, than we now believe.
This was understandable at the time, since it's known that early on in an epidemic only serious cases are noted, and so infectiousness is underestimated and mortality usually overestimated. However, towards march it became definitely clear for most everybody else that covid-19 was fairly serious for many people and the Chinese mortality numbers were not vastly exaggerated.
Because of his belief in an exaggerated infectiousness, Tegnell believed herd immunity would be reached fairly fast. Most of april Tegnell spent on justifying his faulty assumptions, believing herd immunity was to be had in Stockholm in may. To justify this, they used highly dubious modelling and wishful thinking: https://twitter.com/AdamJKucharski/status/125408476749626163...
Sweden currently is now sitting in a horrible quagmire. The infection is still uncontrolled and mortality, though below its peak, is still significant. Testing infrastructure has still not been built out, and is still not done on all symptomatic cases. Likely because the infection was seen as having a similar severity to flu, and therefore it was presumed better to just stay home for a few days, than to go and get tested.
Tegnell can not admit having been wrong, because of bureaucratic honor. The population which are, like in all other countries, generally not very scientifically literate or interested, have not quite fully grasped the situation. But judging by the latest polls of confidence in the government, many are starting to suspect something is not quite right.
I fully support a very open debate, and believe all opinions have a right to be heard. But the Swedish situation should not be confused with science. It saddens me to say, that only very few countries have been more passive, bureaucratic and unscientific handling this crisis. And that seems to have cost quite many lives and much suffering for swedes.