There is an irony here for several reasons. Let me list a few of them.
First, Calypso loves Odysseus and wants to be with him forever. Odysseus is her love slave. In fact, she wants to make him immortal. So, if she could have it her way, she would have him and never let him go.
Second, it is Odysseus who really wants out. He misses his wife and loves her.
Third, the only way Odysseus is able to get off the island is because Athena, the goddess, helps him. She goes to Zeus to ask for permission to allow him to leave. This permission is granted and Hermes sends word to Calypso.
Finally, Calypso is furious at the message that Hermes brings. She comments that the gods hate when goddesses have relationship with mortals.
In light of all these points, it really is ironic that Calypso takes credit for allowing Odysseus to leave.