Download a free analyzer like MediaInfo . Dropping the file into this software will reveal precise technical parameters that tell a story: Encoded Date: The exact second the file was written.
If the video plays but you still cannot figure out where it came from, look at its internal "metadata" (the digital footprint left by the encoder): g9087.mp4
Many cameras (such as older GoPro models or generic dashcams) generate files using a Gxxxx.mp4 sequence. Download a free analyzer like MediaInfo