Salesforce Knowledge User Able to Delete Draft Articles Owned by Other Users When Having Transfer Record Permission

This is working as designed behavior specific to Salesforce Lightning Knowledge when the "Use standard Salesforce sharing" option is enabled in Knowledge Settings. Unlike standard Salesforce objects — such as Account, Contact, Lead, Case, Opportunity, and Custom Objects — Lightning Knowledge allows a user with Transfer Record permission to delete draft articles owned by other users (not just those in their queue).
For context: on standard objects like Account, Contact, Lead, Case, Opportunity, and Custom Objects, a user with Transfer Record permission cannot delete records owned by other users. Lightning Knowledge behaves differently in this regard when standard sharing is enabled.