Don't worry, they didn't. It's true that blood disorders can cause little red spots (or big ones), but the blood tests they did would have shown abnormalities they obviously didn't. So what caused the spots? Most often, nothing in particular--a virus can do it. Allergies don't. My advice is to wait them out. I'd expect them to go away in a week or so. If not, see a dermatologist. But with normal blood results, I can't think of anything serious. There are lots of minor skin changes that come and go and don't mean much.
Take care.
Dr. Rockoff