Reading the supposed plagiarism, I'm skeptical. It looks like phrasing that's commonly used.

It's like saying "the wall was painted white" is plagiarism because someone else said it first.

It's not like he copied paragraphs and claimed them as his own. He used phrases that seem to be a standard way of describing something in the field.

For example:

The line at 2.3.2. Moral Patiency

“On this definition, all moral agents are also moral patients, but not all moral patients are moral agents

that seems to originate from here:https://quizlet.com/348405454/ethics-exam-3-flash-cards/ as

“All moral agents are moral patients, but not all moral patients are moral agents.”

“He then reflects upon how culture determines the moral status of all entities”

that also originates from a flashcard: https://quizlet.com/10587400/ethics-flash-cards/

That it's claimed the origin is a flashcard (and therefore plagiarism) means it is a standard phrase within the field, so standard that it's taught using a flashcard.