3.5 billion people does include the bottom 90%, yes. The 3.5bn number was referring to the fact that billionaires emit as much CO2 as a million people in the bottom 90%. That does include the footprint through their investments, however.
8.3bn people on earth. 90% if that is ... more than 3.5bn? Something like 7.4bn? How can "the bottom 90%" be included in those 3.5bn?
And I also don't follow where the "a million people in the bottom 90%" are suddenly coming from. Which million out if those 7.4bn people?
I'm really at a loss w.r.t. your arguments.