If I bought a packet of "mixed nuts" I would not expect it to have raisins in, but packets of mixed nuts often contain peanuts.

Notice I didn't say "peanuts are nuts because they are packaged with nuts", but because they are included in a package whose label is just "mixed nuts".

See also my other comment here for a number of places where you can see the word "nut" used in a way which includes peanuts (and why it's important)