I am just as baffled. Assuming both had roughly $2000 stacks, S's call was around 1100 into a 2400 pot so he's getting 2 to 1 odds here, barely enough for a nut flush draw in holdem, much less 10 high in Omaha. Furthermore, it's hard to come up with a hand that S has even a 50-50 chance against. Even against a purely random hand he's a 2:3 dog.

So unless D's all-in was relatively small (say 600 or less) the only justification for the call is "i don't think he has any spades", and even then it's borderline. And he better not because he's a 9:1 dog against a naked higher flush draw (no matter how bad you try to make the side cards).

Edit: It's interesting to note that heads up the naked flush draw is enough to justify a call here against almost any hand D has that does not contain a flush draw and that 80% of all hands would not have any flush draw here. It is especially likely that D has no flush draw if S can put him on a set of jacks (assuming the board J is a spade). The problem of course is that you need to have an excellent read on your opponent here and even then it's still a borderline call. Obviously, S is either a great or terrible player. Not much middle ground here.

(BTW, using twodimes and assuming the suits are maximumly favourable to S this is a 70-30 flop in favour of D)