Let's say I frequently lend cash to a wide circle of friends, and they lend cash to me too. Because my memory is bad, I have to keep track of things by writing down the debts on a piece of paper, e.g. "Bob owes me $5, I owe Kathy $10" and so on.
In effect, what these hackers have done is to steal my piece of paper while I'm not looking and scribble "I owe Mr hax0r $10" on the bottom of it.
Now, who have they stolen from? Me, of course! I will blindly pay them out $10 should they ask for it. Has Bob lost money? No. Has Kathy lost money? No. Has money magically been created and cost everyone in the world fractions of a cent? No. I am the person who has lost out.
If they stole huge amounts of money from me such that I couldn't make good on my debts to other people, then others will be indirectly affected too. But I am the person who was robbed.