The important distinction is "Respirable" not "particles". Respirable particles are those that are small enough to get into the alveoli of the lungs. Most talc particles are much larger, >25μm, which are easily caught in the nasal passages or cilia in the throat but there's a huge range of sizes depending on the talc source. Small particles (<10μm) can move to the lungs, hence the air quality warnings at PM2.5, PM7.5, and PM10. Particles of that size are particularly dangerous, but moreso when they contain fibrous silicates like asbestos, which are known to cause cancer when respired.

In the Reuters documents, you see repeated references from scientists / consultants to just swapping the talc for corn starch since it has a larger average particle size and a smaller distribution of sizes -- and importantly, doesn't have any fibrous silicates which can't be guaranteed with mined talc.