I guess chia seeds are really light and sitting on top of your granola. It makes sense to me that you are breathing in as you take a bite and some are making it up into your nose. OR... since you've had a sinus infection they could have been sticking in your throat somewhere when you swallow. Being so small perhaps they will just sit on some mucus
or something else mucus and then when you blow your nose or sneeze they could easily get into your sinus cavity from the bottom. I doubt that they are causing anything more than curosity.
You could make a concious effort to not breathe in when you take a bite... or drink something after eating granola, maybe gargle a bit of water... probably fix it right up.
HEY... it could be worse, it could always be worse.
Human parasites J