Visitor Visa - B2

My husband applied for a B2 visa that we can visit my parents (i am American) in the summer. We live in Mexico and he had all of his paperwork (has worked for the Mexican govt for 10 years, has a car and motorcycle in his name, bank acct, a daughter from his ex wife that lives here in Mexico, etc). Here's how the interview went:
Worker: why do you want to visit the USA?
Husband: to see where my wife is from and visit my in-laws

Worker: do you work?
Husband: yes I work for the govt and have worked there for 10 years

Worker: your wife is American?
Husband: yes and my stepdaughter, my son has double nationality

Worker: how long have you been married?
Husband: we have been married for a month. We were going to get married last year but our son was born.

Worker: oh you just got married then?
Husband: yes

Worker: sorry you need to apply for the immigration visa
Husband: but I don't want to live there, our life is here.

Worker: no sorry

No papers were asked for.

We want to apply again because we already have the plane tickets and plans! He's only going for 9 days because that it was his job allows.

1-What are his chances of getting approved if he applies again in a month or so?

2-Should he say he wasn't able to show his ties to Mexico through his paperwork?

3-Does writing a cover letter really help his chances? Listing what paperwork he has.

Please help!