Actually, these are probably legit.
The Pokemon Dream Radar was an application for the Nintendo DS that was kinda similar to Pokemon Go. Players could use the application to capture Pokemon by activating their DS camera and using it to scan the room and capture Pokemon. With a specific extension, you could encounter the Therian forms of Tornadus, Thundurus, and Landorus.
The Pokemon obtained via the Dream Radar can be caught at levels 5, 10, 20, 30, and 40. Once a Pokemon was caught using the application, they were put in your PC box.
In this video you can see somebody catching a lv. 10 Tornadus.
In your case, somebody probably caught the two legendaries with the Dream Radar and then leveled them up a little bit before trading the game in.
Since the Gen 5 games are now considered "old news", all Wi-Fi connect-ability with the games have been cut. Meaning you can't trade or battle people online, or download the Dream Radar app. So these Pokemon you have are actually pretty valued trade-wise if you can level them up a bit more and transfer them to XY/ORAS/USUM.