That's not what it says at all. This is preliminary and no conclusions have been made. It could be that 4155 COVID deaths were not properly tested and incorrectly categorized.
Now, like all estimates, I am sure there are errors, but it's not like they haven't done their homework.
There isn't enough data in the paper to blame the lockdown per se, however. E.g., it could be that the media fear-mongering is driving people crazy more than usual. There is no way to tell.
I'm glad people are finally admitting that there could be problems with covid testing.