(32,4)1.A The Midrash on this pasuk says that they were claiming "Shi'tuf": that Hashem and this cow had taken them out. If we combine this with a few other Midrashim it kind of works. According to some, the reason a cow came out of the fire is that Micha threw into the fire the piece of pottery that was used to get Yosef's coffin out of the Nile. It said "A'ley Shur" "rise ox", on it. Yosef was compared to an ox in Yakkov's bracha to him. They may then have been saying this form of Yosef will replace Moshe. The way that you could credit Yosef with having taken them out is through another Midrash. In hallel we say "ha'yam ra'ah va'ya'nos"- the sea saw and it ran. The classic explanation is that this refers to the Nile, which saw Yosef's coffin and parted for him. Through this you could say that Yosef also had a hand in bringing the Jews out of Mitzrayim. This may be a possible explanation to what they meant.