We don't know exactly what went on between the 2. Barton's got form for changing room indiscipline but it's entirely possible that Shearer overreacted or decided to make an example of an unpopular player.
It represents the sort of adequate season Arsenal can get away with, as well as the sort of season Liverpool kept putting in pre-Torres. It shows how bent this whole Champions League setup is. The fact is Arsenal (and previously Liverpool) can qualify comfortably without ever challenging for the title. Champions League my arse!