Well at 9 months, I would advise to continue BF as normal as you were directed. But don't be surprised if it comes back up, a lot.
I thought the same thing, it was a complete food, good hydration, etc. My LOs (both still BF, 18 months at 3.5yr) had TWO stomach viruses this fall/winter. For some reason, breastmilk makes them puke. I thought it was coincidence with the first virus, but saw a definite pattern with the second. I even asked the doctor about it. He said it is quite rich on the stomach, that it is good food and good hydration, but it is rich and can cause vomiting. In my kids, it did.
This resulted in a LOT of vomiting in the bed, which is a disaster as we still cosleep. DS only nurses at night, and I didn't figure out that nursing caused it with the first one. DD nurses all day but I would only let her nurse a wee bit during the day (5 min or less at once) to space it out, but at night it's harder to cut her off without waking her up. Well she puked at night, a lot.
Of course, we ended up having to take DD to the dr and he gave her zofran as she was getting lethargic after days of puking everything up. The diarrhea went on for a while too.
Hope your LO doesn't get hit as hard and gets over it quickly!