It wasn't just the last day of the season, it was the last day of his third season with the Packers (1 on PS, two on the regular roster). It does make you wonder, especially when you read that Quarless apparently saw the need to check on him:
They cut Ryan Taylor in October and kept Bostick, even though they didn't trust Bostick enough to put him on the field. Taylor isn't as athletic as Bostick, but seemed to know enough to play. I bet they wish they had him instead of Bostick in Seattle.“I got this guy, you got this guy,” Quarless said. “You know your assignment?”