I don't think it's just the students who need to proof read. I always think it's funny when a teacher says pay attention to grammar and something like this appears in their comments. Especially when they were so adamant about how the paper wasn't all that good.
Really though, I think what bothered (at least Lisa) the most was that when she asked how she could make the argument clearer the tutor said, "Oh, I don't know. I don't really know why I circled those words and why it's unclear, it just is." (or something to that effect) Bad marking? Maybe. She might just be strict, but she should at least be able to say how the students can improve. I mean, that's why we hand in the essays...well, besides the fact that we would fail the course if we didn't.