Yes, you will need to pass smog again. It is mandatory for all used vehicle transfers in California.
You can ignore the seller’s renewal notice because it doesn’t apply to you.
The seller was responsible to get it done prior to sale, but often they neglect to do it on very cheap vehicles.
When a car is sold, who is responsible for the inspection?
The seller is required to provide the buyer with a valid smog inspection certification at the time of the sale or transfer. Smog certifications are good for 90 days from the date of issuance.
The inspection is not required on a transfer if a biennial smog certification was submitted to DMV within 90 days prior to the vehicle transfer date (a vehicle inspection report may be required for proof of certification).
California exempts you as new owner from passing smog only if the vehicle passed smog within 90 days of being sold to you.
There is another exemption for vehicles that are less than 4 model years old.
NOTE: Smog certifications are not required for transfers that occur for a gasoline powered motor vehicle that is four or less model years old. (Determine the oldest-qualifying year model by subtracting three from the current year) the four or less model years old rule does not apply to diesel powered vehicles. A smog transfer fee will be collected from the new owner.