Hygenist explained it a bit differently to me. The presence of blood is the body trying to wash away microbes and other stuff that is getting behind the gum line. The presence of blood (carrying white blood cells) and microbes cause inflammation. FWIW

Hence, no gunk, no microbes -> no bleeding gums after flossing

The other interesting tidbit i learned from that hygenist is that microbes grow on the food and gunk on your teeth, they don't attach directly to the enamel.

That makes sense. I also read somewhere that flossing is not just important to disloge macroscopic food pieces it also helps disrupt bacterial colonies that can set up in between teeth, and every since then I’ve flossed more since I know its doing something even if I can’t see it.