Rabbi Shimshon Rafael Hirsch on the same usage in Ki Sisa 32:7 says that at this point they did not act or regard themselves as Hashem's nation but as people who had been brought out by Moshe. Many of the meforshim state that the original intent of the calf was not avodas zarah but as a symbol for Moshe. Rashi, among others, states that the Eirev Rav were accepted by Moshe Rabbeinu as "converts" to join the Bnei Yisrael in the exodus from Egypt. Had they not been there, the people would not have fallen to the depth that they did. Here, Moshe is pointing out that his compassion in accepting all the (non-Israelite) slaves as part of the people and getting Hashem to accept them is what caused the complete downfall and worship of the calf.