Why do you think your employer needs to know?
You have a work life and a home life.
The basic expectation for the employee is that they will have arranged their personal life such that they can turn up and do the job and go home.
You are not a mother in work you are a worker.
Prior to mothers going into paid employment their job was unpaid child care provider.
Then the expectation was that you will have located and paid a child care provider to take over your old "job" and an employer has no need to become involved in your domestic arrangements.
So just like the new job has no need to hear about how you did your last job unless its relevant to the new role, they dont need to hear about your unpaid jobs, your hobbies or your holidays etc. So is single motherhood relevant if you can turn up and do your job and go home just like any other employee?
Due to the fact that women now fully participate in the paid workforce and that some of them have babies society have adjusted the expectation of how employers should deal with that domestic matter. But a employee with no family or hobbies or non-work life is a more flexable one that a single parent.
We recognise that babies and well adjusted children are a social good and workplaces which are able to adjust to the needs are generally better workplaces.
End of the day the employer needs to treat all candidates the same and you took offence at the CEO bringing it up. (And you dont know if existing workers are allowed adust work days over the school holidays.)