The CA landlord tenant statute starting at Section 1946 addresses the requirements for notice of termination when "a term is not specified by the parties."
http://www.leginfo.ca.gov/cgi-bin/di...le=1940-1954.1
Section 1946 also states:
"It shall be competent for the parties to provide by
an agreement at the time the tenancy is created that a notice of the
intention to terminate the same may be given at any time not less
than seven days before the expiration of the term thereof."
That tells me that if your lease expires on September 30, then it expires on September 30 and it does not automatically renew (unless automatic renewal is specified in the lease) and you have to be out by September.
If there is no termination notice written in your lease, then the minimum notice of non-renewal appears to be 7 days and he has certainly given you more than 7 days notice of his intention not to renew.
Now, read your lease.
By the way, "we were under the impression" is the most dangerous phrase in the English language.