I agree that it sounds like it's the opposite what ASD tends to describe, but I do do the same thing, and I do think that it is ASD related even if the official descriptions tend to suggest the opposite.
I think that what it is is that it's a combination of two things:
1) Difficulty multitasking: You're focused on talking to the person or whatever, so you don't have a chance to focus on what's changed.
2) The details that you care about aren't the details that other people care about. You do notice details, but not the same ones as other people think you should notice.
3) Getting so focused on one detail that's changed, so you can't notice the other thing that's changed.
One time, I was at my parent's house for Christmas, and they asked me what had changed about the living room. I looked around, and did manage to successfully pick out one detail of the room that had changed, but it wasn't the answer they were looking for.
It turned out that the room was basically a mirror image of what it had been before. All the furniture that had previously been on one side of the room was now on the other side of the room. I noticed a detail of the room had changed, but failed to notice that the entire room had changed!
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Level 1 Autism Spectrum Disorder