I blew my nose and there was blood only from one nostril and it was quite a bit of blood. what does that mean?

Superficial vessels: When the lining in a nostril becomes dry,inflamed or thinned superficial vessels can bleed either spontaneously or with the pressure of rapid airflow over the nasal lining. In your case, the lining of your nostril was effected in one of the ways mentioned and you probably blew too hard and a vessel leaked. Blow gently, use nasal saline gel if dry,antibiotic ointment if infection,check with MD.