There are lost opportunity costs (of the space), depreciation costs (wear and tear), and bandwidth still costs money. And now, the AOL PR people have to spend time of this.
I'm not saying these are large costs, but the degree of harm isn't an excuse.
If they needed the chair he was in, they would have just said, "Hey, who are you?" Opportunity cost was zero. Wear and tear would be negligible, and there is no way on earth AOL had to renegotiate their office bandwidth contract because one more person was coding there.
I suspect the AOL PR people are throwing a party that somebody managed to use "young" or "entrepreneur" in the same article with the word "AOL".
Also, degree of harm is certainly relevant. E.g. "No harm, no foul."
I'm not saying it was morally flawless, by the way. It was definitely somewhere between scrappy and duplicitous. And it was probably criminal if AOL really cared. I'm just saying that they don't actually care.
I'm not saying these are large costs, but the degree of harm isn't an excuse.