Firstly, using the word "lockdown" is dangerous, because it isn't just one thing or one measure.
What the study seems to say is that if the restrictions were advisory rather than statutory then people's behaviour and movements would've been broadly the same and thus death rates would have been so likewise, but it's splitting hairs to say that non-statutory measures are not lockdown, and thus a stretch to reach the headline that lockdowns didn't work.
Some of the findings from the report:
- Closing non-essential businesses was estimated to have lowered mortality by about 10.6 per cent, a fall largely driven by closing drinking establishments;
- shutting schools probably also lowered deaths by 4.4 per cent;
- asking people to stay at home prevented 2.9 per cent of deaths;
- border controls roughly 0.1 per cent.
So all in the measures from the first wave probably saved about 20% of mortality by the reports own findings, which last time I checked was more than 0.2%. The final 0.1% on border controls I find interesting considering just how much heat the topic generated on here.
Personally I have my doubts about the idea that people will take responsibility for themselves and thus the measures did not need to be statutory, there are far too many people who IMO wouldn't.