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.
I disagree. The paper goes into some details explaining how many deaths are due to alcohol abuse vs. poisoning etc. They also have a list of conditions that they associate with the various causes of death. For example, if somebody dies of alcoholic gastritis, they classify the death as alcohol-related.
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.