No. It’s not. I have read the whole thing. Several times since I first read it in college.
It IS, because Zipporah was NOT Hebrew. She was a Midianite, and Moses was reared as an Egyptian. Being Hebrew is governed by the blood of the MOTHER,not the father, hence the importance of sarah.
Moses was probably circumcized at birth, but did not know the Hebrew Laws, and it wouldn’t have mattered IF Zipporah had not accepted the Hebrew G-d. Gershom’s circumcision was Zipporah’s conversion and THAT is what sealed the covenant.