Smack is currently only aware of the 'jid' attribute of the actor extension of a MUC item. But recent versions of the XEP also added the optional 'nick' attribute.
Was added to XEP-45 with
Version 1.25 (2012-02-08)
- Added 'nick' attribute to <actor/> element so that an action can be attributed either to a real JID or to a roomnick.