I would think olive oil a poor choice for making french fries. In general, olive oil has too low of a smoke point; it just doesn't get hot enough to fry things well. Maybe the increased pressure made a lower oil temp better? I was always taught to use olive oil as a flavoring on pastas, salads, bread, etc. but never for actual hot-oil-cooking.
It is a poor choice. Best I've found that is readily available is peanut oil. Of course, if you can find it, you could use what McDonalds used to cook their fries in and use beef tallow.