The #Chargers have traded OL Jeremiah Sirles to the #Vikings, source said.— Ian Rapoport (@RapSheet) September 5, 2015
Chargers acquired the Vikings' 2016 sixth-round pick for OL Jeremiah Sirles, source says.— Michael Gehlken (@UTgehlken) September 5, 2015
These things sometimes happen. When a team knows that they're going a cut a player, they'll often let other GMs know that the player is available in hopes of picking up a conditional 7th round pick (although there's no word on what Minnesota is sending back).
This will probably amount to nothing more than if Jeremiah Sirles were released and then signed by the Vikings, but this way Minnesota can make sure nobody else gets him before they do. And if he happens to get called into action during the regular season, they'll gladly part ways with a low-round draft pick, which makes the San Diego Chargers all the richer come draft day.