You are asking the right kind of questions.
I pick:
5. The Guardian should have done the death rate calculation, seen that it is actually low by Western standards, and investigated to see why.
As far as your list goes:
> 1. Your calculation is wrong.
6500 deaths / 2 million people / 10 years x million / 10 100k = 32.5 deaths / 100k people / year, so the calculation checks out.
> 2. Qatar is misrepresenting numbers.
The Guardian isn't relying just on Qatar's numbers. They also used numbers from the countries that the migrants came from.
Regardless, that's one of the thing they should have investigated when their numbers gave such a low death rate.
> 3. Qatar has safer working conditions than US.
The deaths the Guardian is reporting aren't just deaths at work. They are how many migrant workers died regardless of cause while in Qatar.
It is quite possible that Qatar has worse working conditions than the US, and has a much higher at work death rate than the US, but has a much lower death rate outside of work.
In the US significant fractions of the deaths of young males are poisoning (drug overdoses falls under this), suicide, automobile accidents, and homicide.
Qatar has a very strong anti-drug policy, with harsh penalties and little tolerance. Their drug death rate is about 1/25th that of the US.
They are also quite intolerant of drunk driving. If you are in an accident you are considered drunk if there is any detectable alcohol in your blood, even if the accident was entirely the fault of the other driver. That's so low a tolerance that one drink the night before can count as drunk driving the next morning. I'd expect then that they have a much lower automobile accident rate. (Also I'd expect most migrants use other forms of transport).
Qatar also has a very low homicide rate (about 1/20th the US rate).
For 3 of the 4 top non-medical causes of young male death in the US, Qatar likely has a much lower death rate. Is that enough to offset any higher death rate at work sufficiently enough to bring the overall death rate down to well below US young male death rates?
I don't know. I should know because the Guardian should have covered that.
> 4. The reality is absurd.
The Guardian is absurd in this case.