Where did the Raiders play their home game this past Sunday?

It was indeed at the usual home field, the O.com Coliseum. The reason you didn't see a baseball infield is because after the Athletics' season is over, the infield gets filled in with grass because the stadium no longer has to be converted from baseball to football and vice versa. This is one of the problems that arises when teams from MLB and NFL share a stadium. The Dolphins also had this issue in Sun Life Stadium, but they won't anymore as the Marlins will be moving into their own stadium starting next season. The Eagles, Steelers, Jets, and Vikings had the same issue for years when they shared stadiums with the Phillies, Pirates, Mets, and Twins respectively. The first Browns franchise dealt with that problem before the Indians moved into Jacobs (now Progressive Field) in 1994. The Colts dealt with it in Baltimore before moving to Indianapolis. The Houston Oilers also dealt with it before moving to Tennessee in 1997. The Arizona Cardinals worked with it while in St Louis and the 49ers saw their dealings with that issue resolved in 2000 when the Giants moved into AT&T Park. The Seahawks rejoiced in 1999 when the Mariners moved into Safeco Field, and the Padres move to PETCO Park in 2004 made the Chargers ecstatic. So as you can see, this is nothing new, but is something that is rapidly coming to an end. With the Marlins move, the Raiders are now the only NFL team that still shares a stadium with an MLB team.

They were at Home at the O.Co Colliseum

You don't see a baseball field anymore because they covered it up since the A's season ended.

I'm pretty sure it was at their home stadium the O.co Colliseum