The right to be forgotten applies to any entity collecting and controlling data. Basically, the right says: Delete all data on me that you're not legally obliged to keep.
If you think of Facebook and wanting to close down your account there, it makes sense. You don't want them to keep your photos and likes forever. With a shop, if you only collect the necessary information to process the order, it doesn't make that much sense. If you profile your customers, however, it does, because the customer will want the data/profile deleted.
For us small shop owners and thirty bees, it basically boils down to the understandable wish of: I don't want to have a login at your shop anymore. It doesn't have anything to do with orders per se.
However, what it does mean, and this applies to guest orders equally, is that after you are no longer legally obliged to keep the order data, eg for tax purposes, you must delete it. With a customer account you could argue that the data may be kept as long as the customer has an account, as the customer will have an interest in seeing their order history. But once the account has been deleted, or where it never existed because the orders were places as guest orders, the data may *generally speaking) only be kept as long as you are legally obliged to keep it.