"The knight was injured."
Translation:Ο ιππότης τραυματίστηκε.
Yes, injury does not implies blood every time. Τραύμα, trauma, traumatic, is a medical term, and it is used for everybody that has an accident, even a broken leg or a toe. No blood at all. Πληγώνω or passive πληγώνομαι, and the noun πληγή means mostly blood, one never can say o άνθρωπος έπεσε, έσπασε το δάχτυλό του και πληγώθηκε. In this very case, yes, they can be be used as synonyms. Even we don't know how much and how serious was this injury we can imagine that he had a blood-shed in a fight. Even there was not actually.
Notice that πληγώνω is more poetic and can be used for a bad experience as a failure in love :) ;)
let us look form the perspective of the course users. A person who wants to learn Greek, do they want to know the precise correspondence between injured, wounded, hurt, etc. vs πληγώθηκε, τραυματίστηκε, κτυπήθηκε κλπ or do they want to get the idea that something bad happened to the knight/ιππότη? My humble opinion is that DL should be very liberal/forgiving/accommodating when it comes to evaluating the users' response (in Greek and in all the courses).
My point is that synonymous words are never exactly the same: you cannot say "an open injury" or "ανοιχτό κτύπημα" for this reason. An injury is generic word like hurt, although hurt is less serious than injury. Finally the words injury and hurt can include wound but not vice versa: an injury might be a wound or it might be a broken bone, while a wound can never be a broken bone.
P.S. On the subject of strictness I agree that DL must be lenient but up to the point of not letting its learners confuse the meaning of words or phrases and this is indeed a difficult proposition.