I've just had this happen to me. I made a video back in March and just a few weeks ago it started getting views and still is. I went from about 400 views to about 10,000, and it's still going.
Turns out the video was embedded on a website called SkidrowReloaded, which after hunting it down is a cracked games website. Whoever uploaded the game used my video as the preview. Games are heavily pirated in Russia so it's no surprise why most of the views had come from there too
I've got a handful of subs from it but nothing crazy. I don't agree with the use of my video but I'm not complaining, high views means high search ranking so actual viewers will come that way.
Sidenote: If a video is embedded somewhere the likelihood of receiving comments, likes and subscribers is quite low as the people watching aren't on Youtube to properly interact.