Sounds bad. But almost certainly was not simply a spur of the moment decision, but rather that Lenz was on the list of people to be fired later in the day and had done things that Armstrong knew about (like leaking Patch information). Still bad to do it like that on a call where people are getting fired for real, but this gives some context.

http://www.businessinsider.com/aol-ceo-tim-armstrong-appeare...

  A few minutes later, Armstrong complained about leaks to 
  the media. He said the leaks were making Patch seem like 
  "loser-ville" in the press. He said, "That's why Abel was 
  fired." "We can't have people that are in the locker room 
  giving the game plan away."