It wasn't much of a surprise, he won it within the margin of error of most polls.

Super Tuesday is forecast to give Sanders ~50% of the available delegates (I mean delegates available in those states, not the total) but there is a lot variance possible due to the 15% threshold and so many candidates still in the race. Assuming he does get 50% or more, it would make his path to the nomination easier.

Biden can win a couple of southern states on Tuesday, which may not help him much, but if he wins or comes close in Texas (second largest to California by delegate count) then he can put a dent in Sanders' 50%.