Personally, I would offer to pay for it by contacting ESDG, and perhaps they might be kind and offer to let you have it, but if not, still the *right* thing to do is to pay for it, but then again thats just me. hell, I am one of those that if I go grocery shopping and forget to take the items off the bottom part of the cart, and the checkout person neglects to charge me for them, I turn around and go pay for them.
Think about it this way. Companies make errors all the time. They are not infallable, however, this IS their livelyhood, and paying for something that one accidentally gets, helps keep them in business, and helps keep costs down.
Besides, the Citation X is the best payware biz jet out there, and its worth every penny they ask.
And yes I know the cost of some payware has steadily gone up, but you have to consider, that there are several companies that are "raising the bar" in what is offered, and as my father always used to tell me "you get what you pay for...you can buy a piece of furniture from Wal-mart for $100 that falls apart eventually, looks like s***, or you can go to a craftsman/woodworker and pay $1000 for something that can be handed down for generations as a work of art"
Use your own discretion and ponder this. if you dropped a $100 bill on the ground without noticing and someone behind you picked it up, would you hope they would return it or keep it?

As Dave said, its up to you. Consider yourself lucky, or offer to pay for it
---Stephen