Most of the people we now know to have been supporting Obama were not public supporters of Obama in 2008 - nobody wanted to get on the Clintons' wrong side. Hillary also had superdelegate support and recall that she hinted at winning the nomination on the convention floor with heavy superdelegate support.
Voters definitely saw Obama as an outsider. Even his theme was "change is here".
This.
Obama did have support from the Party elites. That doesn't make him the establishment candidate in 2008. That year, Hillary Clinton was.