Charges made through the Stripe Add-On have shown up flagged as “recurring”, when they are not part of a recurring subscription plan.
Stripe have confirmed that this is an expected behavior when the storage of customer card details is required.
The “recurring” flag in this instance does not necessarily indicate the customer is subscribed to a recurring billing plan, only that the card was saved for future charges.
Cards attached to non-recurring transactions cannot have all details stored, in keeping with PCI compliance requirements. Therefore the recurring flag must be used by Stripe in order to store card details for future charges, even if future charges are not automated as part of the plan.
Stripe have created this document to explain the change: https://support.stripe.com/questions/non-recurring-charges-show-as-recurring-on-customer-bank-statements.