I think the answers to these questions are unfortunately a bit muddled.  Initially I was going to say that the Public Relations Officers who wrote those articles may have inserted the term without thinking (or knowing).  However one possibility is that since ISAF is a reaction to the Bonn Agreement, it may be considered peacekeeping with the parties including the fledgling national government and the various quasi-legitimate warlords.  But the Taliban and Al-Qaeda are not parties to any agreement.  To my understanding, without an agreement in place between sides, there is no peacekeeping.  "Security Assistance" (the SA in ISAF) to me is a subset of the military term "peace support operations" (peacekeeping is another subset of peace support operations).  In the end, I think the NATO and ISAF webpages must be authoritative, and I have seen no mention of the term "peacekeeping" on any of the main documents I have looked at.  I don't claim to be an authority, and soldiers (and bureaucrats, and politicians) argue about the meaning of words all the time, but to me 'peacekeeping' has a specific meaning that ISAF does not fit.