The ratio less than 2 : 1 in Cu$_2$O shows cuprous (Cu$^{+}$) ions have been replaced by cupric (Cu$^{2+}$) ions. For maintaining electrical neutrality, every two Cu$^{+}$ ions will be replaced by one Cu$^{2+}$ ion thereby creating a hole. As conduction will be due to the presence of these positive holes, hence it is a p-type semiconductor.