MSNBC's Steve Kornacki tweeted out this tidbit from the early exit polls, and it's being interpreted around Twitter as good news for Hillary Clinton — which it may well be! But there's no particular reason these preferences should lead to a Clinton victory:
Do you prefer...— Steve Kornacki (@SteveKornacki) March 1, 2016
Political experience: 80%
Outside establishment: 16%
(cumulative exit poll)
Bernie Sanders has held elected office almost continuously since 1981, when he was elected mayor of Burlington, Vermont. It's a bit hard to compare that with Clinton's experience — she was clearly more involved in her husband's various administrations than most first ladies are, so it's misleading to say her experience only began when she was elected to the Senate in 2000 — but Sanders is arguably a more experienced politician than Clinton is, and he's definitely a very experienced politician.
But the deeper point here is that the opposite of "outsider" is "insider," not "experienced." Plenty of extremely experienced politicians operate outside the political establishment: Bernie Sanders is an example in the Democratic Party, but Ron Paul was an example in the Republican Party.
Conversely, plenty of insider political candidates are pretty inexperienced — Marco Rubio is clearly the candidate of the Republican establishment even though he's only been a national political figure since 2010, and Barack Obama won over much of the Democratic establishment in 2008 despite having even less political experience than Rubio.
All that said, I'd guess these results are good for Clinton, but in a somewhat odd way. We tend to interpret poll results like these as voters explaining the reason for their choice, but they often represent voters rationalizing their choice.
The Clinton campaign has emphasized Hillary Clinton's experience, and so voters who like Clinton are likely to echo that argument for her back to pollsters. By contrast, the Sanders campaign hasn't emphasized Sanders's experience so much as his outsiderness, so we would expect that voters who favor him are less likely to tell voters their decision was driven by their candidate's experience.