Note the "at least 99.97%" in the definition of HEPA. So, as you imply, I'm sure the S/X filter meets that spec.
It might exceed the minimum spec.
If it exceeded the minimum HEPA specification then they'd have said it exceeded minimum HEPA specification. Wouldn't they.
Hint: it doesn't exceed the minimum HEPA specification.
So, maybe it's "just" a HEPA filter. Or maybe it's a particularly high-spec HEPA filter. Who knows?
It's a HEPA filter sourced from a company that makes HEPA filters. Because, strange as it may seem, Tesla doesn't make HEPA filters.
I believe the mode also involved over-pressuring the cabin so that all the cabin air could be guaranteed to have been filtered.
Create positive cabin pressure by running the blower? You mean like, every other car.
You've also not explained why this feature is no longer presented as "Bioweapon Defense Mode" and has become a far more ordinary sounding "filtration system". Could it be that "Bioweapon Defense Mode" falls into the same category of mug-exploiting twaddle as "lowest probability of injury" which caused Tesla to be on the receiving end of an NHTSA cease 'n desist?