By compared to itself it means the motions of the atoms within an object relative to each other. The object itself can have any velocity depending on the observer but no matter which direction it's moving as a whole or how fast, the atoms within still have the same motions relative to each other, which is signified by temperature.

Location is indeed a way to distinguish identical particles, however if two identical particles share the same location then there is no way to distinguish them. You can not say "which is which", only that two particles came in and two went out.