Hello Shaun,
Good question. WooCommerce Tickets and Events Calendar PRO are two separate plugins, each with their own features. You can certainly use WooCommerce Tickets without Events Calendar PRO and use it with the free The Events Calendar plugin instead.
If you do want PRO’s features in addition to selling tickets, then you will indeed need to purchase it separately.
Does this help clarify things a bit? Please let me know and thanks for checking out the plugins!
Geoff