Question:

Why are Entry Actions on a document being triggered when a user cancels a document workflow in Vault?

Answer:

This is working as designed. If a document is in a state that has Entry Action configured and the Workflow Cancel State is set to State in which workflow started, then the Entry Actions will be triggered when a Document Workflow is canceled. 

To prevent Entry Actions from triggering, the Workflow Cancel State needs to be configured to either be No state change or a specific state (that does not have Entry Actions) per business needs. 

Related Documentation:

Vault Help Documentation: Canceling Document Workflows 

Vault Help Documentation: Entry Criteria & Entry Actions