It could go both ways. normal people do talk and do activities and work at the same time -

For example

someone takes notes while talking in a meeting
a parent is bathing one child while directing the other child how to dress themselves
a parent cooking dinner while helping a child do their homework
someone usting their house while their best friend is sitting at the table having coffee

It is completely normal for people to be doing one thing and talking on a completely different subject and in doing so does not always remember what was said during the conversation.

and it could also be a part of dissociating since having memory loss and time loss is some of the criteria for a person with dissociative disorders.

The way a professional in the field of DID explained it to me is that it falls into the dissociative catagory if there was something upsetting and triggering about the conversation that made the person need to mentally escape the conversation for example the person starts feeling attached by the person or they are having the conversation with, the topic of conversation is causing the person to feel panicy.

Dissociation beyond the normal level is using daydreaming (imagry and relaxation techniques) mentally escape a situation in which the person percieves as being a danger to them.