A Knowledge User is able to delete draft articles owned by other users when having Transfer Record permission in Lightning Experience.
This behavior is working as designed. The behavior described is specific to Lightning Knowledge when enabling the 'Use standard Salesforce sharing' option in Knowledge Settings.
For example, in Account, Contact, Lead, Case, Opportunity, and Custom Object, a user is unable to delete records owned by other users even when having Transfer Record permission.
Transferring Records
Choose the Sharing or Access Model for Lightning Knowledge
Considerations for Changing a Record’s Owner
000392252

We use three kinds of cookies on our websites: required, functional, and advertising. You can choose whether functional and advertising cookies apply. Click on the different cookie categories to find out more about each category and to change the default settings.
Privacy Statement
Required cookies are necessary for basic website functionality. Some examples include: session cookies needed to transmit the website, authentication cookies, and security cookies.
Functional cookies enhance functions, performance, and services on the website. Some examples include: cookies used to analyze site traffic, cookies used for market research, and cookies used to display advertising that is not directed to a particular individual.
Advertising cookies track activity across websites in order to understand a viewer’s interests, and direct them specific marketing. Some examples include: cookies used for remarketing, or interest-based advertising.