I think this might be the "Vested Veteran" rule at play. If a player (with a minimum 4 years of NFL experience) is on the roster for the first regular-season game, their base salary locks in as 100% guaranteed, meaning the team is on the hook for the full amount even if they release the player the very next day.
I think Alford will do the job week 1, then Greg Dortch will take over once his salary won't be guaranteed.