Absolutely stupid that when you unlink an account the underlying data is silently lost. However due to GDPR and similar laws, irrecoverable delete is absolutely a thing. They cannot recover your data if it went through the same process of forgetting it as they would for GDPR, and there's a good chance the system wrongly treats the unlinking of Twitter as a request to forget. If they can somehow recover the data for you, they have a flawed architecture for forgetting your data, and they will not give that up as easily.