It's the pattern used at https://github.com/cmaish/JabbR/blob/6508b25c2c93515660efcbc8087502ae9a02b9da/JabbR/Chat.ui.js#L1625 to only add a livestamp if one doesn't exist.  This change is here to make it so that when you /afk the number of minutes since you went inactive are shown to users who are in the room (to make AFK behave more like the regular idle).