No. It is not for PhDs only. Please read this paragraph in the petition:
"We, the undersigned, Citizens, Permanent Residents and Temporary Residents of Canada, call upon the Minister of Immigration, Refugees and Citizenship to take measures to give priority to international graduate students in the application process for permanent residency, such as adjusting the comprehensive ranking system to award more points to international students who study inside Canada and/or allowing work experience under a study permit to count towards work experience in Canada."