I think you have an angle in the ownership of real estate in an impacted county. But my recollection is that the guidance says that if the taxpayer has a trade/business in an impacted county, he is eligible for the extension. If so, then we get into the issue of whether the rental is a trade/business that qualifies for relief, as mentioned by NoCal, who posted while I was typing.
The fact that he uses a CA address I don't think is determinative. If you file with a CA address, you are not eligible. But...the chances of getting caught are very low, considering that he files a resident return. But you should not advise him that the CA address secures relief.
What might be of interest to you is that this whole issue has been discussed quite extensively on a list-serve that I think is affiliated with the Cal Soc of CPAs, so there are many CA practitioners. People are not excited by this whole thing. The consensus is that we are expecting to have to deal with many notices where IRS or FTB computers are not properly programmed. Interest is being assessed at 7% for underpayments? That is going to cause clients with large balances heart attacks. If there is an underpayment from Q1 - Q3, there is disagreement as to whether interest continues to accrue during this period of forgiveness.
Many practitioners are not even telling their clients about this. I have taken the other approach because I don't want my clients to hear about it elsewhere and wonder why I did not tell them. I am telling them that this extension of filing and payment is available, but no one expects it to go smoothly. That unlike the Covid extensions, this is not country-wide. That it will take time, and therefore money (our fees), to sort out any assessments that are automatically generated by computers that were not properly programmed, and that unless they expect to earn substantially more on their money during the deferral period than what it will cost to pay me, they should just pay according to the regular schedule. Many of us are filing extensions even though not required to avoid dealing with potential notices regarding late filing.
I have a client with about $4M due 4/18. I explained all of this to them. People who have that kind of balance due have so much money that what we think is a huge amount of earnings potential is not that significant to them. They are going to pay on schedule because they just don't want any headache.