Definately sounds like an interesting chat Bikerbeth. Its weird how the brain can mix up and alter memories like that. Like sarasa said probably sundowning, or maybe the dentist visit and trip out excited and tired her brain a bit more than normal so she couldn't keep track of the past as well as usual.
Mum often mixes up timings from the past as if they all happened at the same time, like when I'm her friend (from 30 years ago) and her mum has just died (from 45 years ago) but she lives with her mum who is still alive (53 years ago) and also has 2 daughters in their early 20s which is about (25 year ago). All different time frames but they can all be happening in the same conversation at the same time. It can be quite mind boggling to keep up with. Its often in the afternoon when she gets most mixed up sundowning, or on days where done things or has somewhere to go/something to do.
Other times she mixes up things she's seen on tv or read in magazine into her conversation, like when she asked if hubby was going to leave work now he wasn't going to be a prince when she'd seen on news earlier harry and meghan wanted to step back from royal life and one day she asked me about my dolls and how many I had now, I eventually remembered she had read about a lady in take a break earlier in the day who had about 10 or 11 reborn dolls she dressed as babies and mum thought it was me.
I dream a lot and usually remember one or two the next day (though not as much lately) when I first remember them I think well that was weird but as I think about them I can usually pick out little bits from that have reasons they are in my head, like something I saw on tv, read about, did or talked ,or thought about the day before. I quite like figuring out where the bits came from and when mum has weird conversations I tend to try and do the same. It serves no purpose, it doesn't matter to mum and most times unless she asks why did she say that I don't even tell her, but I like to know reasons for things and I just like to do it .
I'm sorry I seem to have rambled a bit there, and gone a bit of topic I think too
Anyway it sounds like an interesting conversation and although it was probably sundowning or a bit of over stimulation its good that your mum seemed happy enough and enjoyed being out with you and felt settled when she returned home. x