Since Johnson was waived injured with a hamstring problem, it seems to me that we didn't necessarily pick him up to see him play Friday but to stash him on IR for next season.
Of course, we could have already seen enough in scouting him to want him on the roster, but I think that's unlikely since we don't know if he'll be ready for the regular season and can't afford to use another roster spot on a player who will be sidelined. Plus, he's making the move to LB and we don't know how that will go for him.
If he has PS eligibility, we could be picking him up to have his rights if he clears waivers, but since I don't think he would, I don't think Dallas doing that would be likely.
Maybe he's just not that injured, but enough for Indy to have to waive him injured?