I cannot answer for Riverside County,
but I would bet that it's the same as Fresno:
The Escrow charged you 1 or 6 month's of taxes, based on the old tax rate.
You were probably given an ADVISORY about a SUPPLIMENTAL TAX, which told you that you would receive a NOTICE from the Assessor about a Tax change.
You probably will be paying less, based on the new selling price; but the adjustment will take a few months. You may even see a Credit.
If you are impatient, you can always go down there and ask them.
Good luck and congratulations