Maybe it's that they were intending to address a group, but then realised that what they said might cause offence so they corrected themselves.

I think it's not so much they imagined what they were saying before they said it, it's that they reached for the handy phrase for addressing a group without thinking, and then only afterwards realised it. At least that's what I would do.

I wonder what it would feel like if I joined a majority female class and was addressed as "good morning ladies, and man". I've never been in the situation unfortunately.

Another phrase would be good. I vote for youse all.