Or he could have been strapped into a chair. They do that as I understand it.
Or the question could be running and/or cutting without stability issues or pain.
You simply have no basis to believe whether PUP is cautionary or whether his injury is potentially career ending.
Bishop suffered a hamstring injury that required surgical repair that effectively ended his career. A year on IR, then 6 games played over 2 years, and then he was done. Everybody was counting on him coming back for 2013 until he was released in June of that year. Or think about Bishop's replacement, D.J. Smith. While a lesser player than Bishop, Smith was nonetheless a starter who tore an ACL and was effectively finished, playing 2 games over 2 seasons with no starts after injury.
Correct me if I'm wrong, but I seem to recall you were enthusiastic about Benson coming back in 2013 after going IR with what was initially reported as a "foot sprain" but was subsequently diagnosed as a Lisfranc injury. He never took another NFL snap.
Injuries requiring surgery are a crap shoot, especially when talking about guys like Barrington, Bishop, Smith or Benson. Whatever these players' virtues, any special athleticism is/was not among them. Seemingly small diminishment in athletic ability can suddenly be a disqualifier for guys like this. Veteran guys with athleticism to burn and veteran smarts can adapt; perhaps Nelson would be one of those guys if he's never 100% his old self. Barrington is not one of those guys.
But lets not be so glum. We have absolutely no idea what is going on with him...only a broad range of possibilities.