It's hard to tell whether this is a response to a job ad or this person is just casting a wide net in search of a particular position. I suppose you could search the local classifieds and online job sites to see if there is a wanted ad for a post within your company. You could also just ask your boss, though that could turn into a rather uncomfortable conversation if he is actually looking to replace one of you, and is attempting to do so on the sly.
Were you able to get a look at the application itself? That would probably tell you what you want to know.