Yes, one could argue that anything that you see is nothing more than reflected light, but the point I'm trying to make is that you wouldn't be able to differentiate this from anything else. And this is an important distinction. From such a distance you wouldn't notice the momentary glinting reflection and surmise "oh, look at that fly!" No, you'd barely even consider it. It could be a mote of dust or a water droplet 100 feet away for all you'd know.
Conversely, if you knew there was a fly there and someone could somehow increase it's luminosity (just for the sake of argument) until it could be seen at 100 miles then at a certain point you could 'see the fly'. Not literally of course, it would still be the light that you're seeing however I'm thinking that is just semantics.