Section 24007 (b)(2) of the Vehicle Code states it is the responsibility of
the seller to provide a valid smog certificate at the time of delivery of
the vehicle. There is no provision in the law to sell a vehicle "as is" as
far a the smog inspection is concerned. Therefore the seller is always
responsible for the smog check even if they mention the car is sold "as-is".
Assuming the purchase took place in California (even though the car is from
Oregon) the seller has to follow this law.
The release of liability document the seller completed and sent to the DMV
only releases them of liability as far as parking tickets, accidents,
vehicle code violations and so on; basically only things that you do with
the vehicle after the purchase. It DOES NOT release them of the liability
from following the law which specifically states he or she is required to
give you a passing smog check certificate along with the vehicle when you
bought it.
Unfortunately, your option at this point is to pay for the repairs necessary
to get the car to pass the smog check and then take the seller to small
claims court to recover your costs. Although the law clearly supports the
buyer, collecting on a small claims judgment can be difficult, so the
amicable solution is usually best.