Yes, you are correct. Some of the people who develop pneumonia can have had it because of COVID-19. And some have it because of the flu or other respiratory illness. A test positive result for SARS-CoV-2 doesn't mean you have COVID-19. Many results are false positives, and some are positive without even being sick. This information has been coming out in the msm. When COVID-19 began being reported, the flu dropped off from reports in April 2020, months before other years. It's almost as if cases of the flu were being reported as COVID-19, as per the CDC guidance to presume or assume COVID-19 just because you think it is, as one can easily say the flu symptoms are COVID-19.
So if someone died of pneumonia, it doesn't mean it's COVID-19, but it could be. If you have pneumonia, you have another illness, making you not healthy. What I said was that the 6% of people dying of only COVID-19 as per their death certificate are assumed to be previously healthy. If you have another illness, you aren't previously healthy. Did you also know that some of the additional causes of death included with some COVID-19 death certificates, include poisoning, injury or even self injury? What does COVID have to do with you dying from poisoning or suicide? Yet that gets counted as an alleged "COVID death".
Here's the statement early in your thesis that was fundamentally flawed, IMO:
But a cause of death isn't necessarily a pre-existing condition.
Since you were polite in your reply, I did some quick research tonight. 55000 of the death certificates in question had "respiratory failure" listed as a cause of death. This is apparently because they typically list the physiological process which caused the death. Of course, it is not difficult to deduce that most of those respiratory failures were caused by COVID-19.
To your 2nd point, about mis-diagnosis of flu deaths as covid deaths, I suppose it certainly can occur in some cases. I don't know how many times they re-test a patient with serious problems to see if he's actually suffering from something else and only had a single false positive test that pointed at covid.
But I think it's obviously false on the face of it to assume that the flu can account for a large portion of the deaths assigned to covid. First and foremost, this is clearly not true just because we didn't have nearly so many flu deaths. In 2018-2019, we had 34,000 flu deaths in the entire year. In the previous year, we had 61,000. As a macabre side note, those numbers are from a rather laughable US News & World report from Jan 2020 where the author was literally trying to convince us we should be more worried about the flu than coronavirus (that's the title of the article).
Now I know you mentioned other things listed on the death certificate such as poisoning, injury, and self-injury. Injury seems pretty basic to me: people suffering from serious diseases are much more prone to injury. And I suppose someone in a suicidal state of mind is much more likely to be suicidal when suffering from a debilitating illness. And more likely to accidentally poison themselves by ingesting something they shouldn't due to lack of mental acuity (e.g. mixing up pills).
There's many possible explanations, and we just don't have the facts to analyze the data. But the doctors who wrote these reports did have the data. And they made their determinations as to whether to classify the deaths as covid deaths. So, short of analyzing the data myself, I think it only makes sense to assume that the doctors that made these determinations are likely correct in their assessments.
Now it's possible you believe that we're being presented with false data by the medical establishment for ulterior motives. You didn't say anything like that in your post, however, so I didn't think it worth addressing. But if you do think that is a root issue which undermines my argument in the previous paragraph, I'm happy to debate the point.