I get this on some of my cameras when I forget to switch back from movie mode to still mode. It's the camera doing it, not Classic. Classic as already said cannot just generate random jpegs during import so they were already on your card.
In camera file saving issue? Issue is more complex than what follows, but keeping it simple.
Even if you shoot RAW only, some situations, typically involving advanced filters (aka toy mode) or in Camera PANO, video , some forms of special shooting, may result in a JPEG being created, not a RAW.