Malik Jefferson had a much better pre-season game at the Giants than in the pre-season game in Kansas City, in which he suffered the injury that led to the Lions placing him on Injured Reserve. I incorrectly mentioned that Jefferson was placed on Injured Waivers. That category isn't applicable to Vested Veterans, which Jefferson is.
I believe that Jefferson fell behind Ben Niemann in the Lions LB pecking order and he easily could have fallen behind Ty Summers. The Lions do have the option of bringing him back in a few weeks. If that did happen, the P.S. would likely be where Jefferson is signed to at first.
The two players the Lions signed provide the Lions with more depth for the pre-season finale. Both have an uphill battle to get P.S. opportunities with the Lions next week. But one or both could realistically get a P.S. opportunity with the Lions later in the season.