How is it possible?

I recently found an object (65prim) on my land that says it belongs to me, however I never placed it, nor would I. How is it possible that this could be attributed to me without my knowledge or permission?

That shouldn't be possible, Threshin. I presume you've already ruled out the possibility that it was set to share with a group too, or "Allow anyone to move", even... and of course it can't be Physical because it's >31 prims. Or that another object you own may have rezzed it.

However, if this repeatedly reoccurs, it quickly becomes easier to find a solid reproduction and figure out what's going on. Any such confirmed errata, if in fact the case, should be sent in as a bug report via the Help menu.