And it looks like the inventory already contains exactly one pack. Click "Break
Minifigs" and then sort by item number and you will see all the parts together.
Not necessarily. They could have received a mispacked bag with an extra. It
wouldn't be the first time Lego's machines have made an packing error.
I had an extra minifig part in a recent set that wouldn't normally be an
extra.
This piece is one of a group of parts that comes as a unit. To get an extra one,
you would need to get an extra entire pack:
I've never seen a mispacked multipack of parts. Not saying it couldn't
happen - there are some pretty weird extras that pop up from time to time - but
the likely/normal scenario is that the submitter missed the one on the fig while
counting, or wants to move the one in the regular section to extra since it wasn't
used in the model.