Are people dumb or what?

This is a phone call I had yesterday.
Me: Hello
Doc office: Is this Kim?
Me: This is Kimberly
D.O: Hi Kim. This is so & so from the doc office.
Me: It's Kimberly actually.
D.O: Oh I'm Sorry, Kimberly
Is it that people are dumb, rude or they just don't pay attention? Or maybe they just don't care about anything?