I would suggest worrying much more about PM2.5 and getting a filter that does trap those particles. Many health problems are caused specifically by small particulate matter.
His statement "I'm not concerned with the ability of the device to remove PM2.5" comes across as dismissive - he's not concerned because he's using a HEPA filter health officials are recommending and therefore he trusts it. HEPA starts at 0.3μm ("PM0.3") particle size, which doesn't cover finer forms of elemental carbon (soot). "H13" is a minimum retention efficiency though, not a specific particle size or application.