I could argue it both ways (theft and non-theft) which, for me, puts it into the ethically 'grey' area of interpretation.

I would reason to 'non-theft' based on an argument that AOL gave access to the building (badge) and provides services for people with access to the building, therefore giving access was tacit agreement to the use of the facilities. Other employees no doubt sleep there on occasion and that it also tacitly allowed. Therefore non-theft.

I would reason to the 'theft' conclusion that AOL provides services to incubators and to employees but does not explicitly extend employee benefits to incubator attendees. Using services and consumables that are provided to AOL employees is outside the scope of services offered to incubator participants. Therefore Theft.

Eric was aware of this grey area, clearly trying to stay outside the regular patrol of security, and thus actively trying to not force a resolution on the question of allowed or not allowed. His response when the resolution occurred appears to be 100% compliance.

If I were considering investing in Eric's activities I would consider both parts of that story, the first where he exploits a grey area and the second how he responds to being discovered.

In my experience it is people who take Eric's approach of interpreting grey areas in the most optimistic way until shown otherwise, and being 100% rule following on explicit rulings, are successful. There are thresholds of course, if there were signs that said "No one is allowed to sleep in this facility" or "At no time will anyone spend more than 12 out of 24 hrs in a day in this facility" or even more general guidelines that define a standard for defining 'living on site' and a express a prohibition against it. Something which might say "You would be considered to be living here if you spend more than 100 hrs a week or do more than 3 loads of laundry or sleep more than 12 hrs a week or eat more than 12 nominal meals at the facility" etc. AOL could call it out, but they haven't. And that leaves it open to interpretation.

In the business world that is sometimes called 'moxie' or 'stones' or any number of euphemisms and its generally respected.

What is not respected is explicit exploitation. So for example when I worked at Google the mini-kitchens all had refrigerators that were full of beverages. A small number of employees were found to be exploiting this 'perk'. An example of that which was given was an employee that prior to the weekend, would take an empty back pack and fill it with anywhere from 20 to 50 beverages to take home. That was 'theft' in the sense that the intention was for the beverages to be enjoyed at work not at home, even if you were working from home. But it was theft because of the quantity not because of the taking. Taking one beverage to drink while riding the shuttle home? Not a problem although you were not 'technically' at work any more.

I think Eric intentionally interpreted the situation in a way that would support his actions, and recognized that those actions might not be completely inline with the intent, and waited for AOL to express its intent. I don't think he ever believed AOL would 'endorse' his living on campus while he worked on his startup (incubator participation not withstanding) but I could see a case for it being an open question if not explicitly disallowed.