No, this isn't about Joey Bosa. Believe it or not, the Chargers do have other players on the roster. They've just added a new one, signing C Bruce Johnson after waiving-injured OLB Tyler Marcordes, who was almost certainly going to be on the list of first cuts anyway.
Johnson is an interesting choice of a player to add. He was picked up as an UDFA by the Eagles but was waived earlier this week. That doesn't automatically mean he's not at the required level - Branden Oliver was an UDFA who got waived in the preseason by the Colts in 2014, and their loss has very much been the Chargers gain.