No, this is not true. If you have been authorized reside in Canada for at least a year, you MAY select CPP-O. Or you may select the visa office that serves your country of nationality.
Just read the application instructions -
http://www.cic.gc.ca/english/information/applications/guides/5609ETOC.asp
Indicate the name of the Immigration Office which serves:
your country of nationality, or
the country in which you are residing, provided that you have been lawfully admitted to that country for at least one year. (e.g. CPP-O if you have been admitted to Canada)