Does it sound as though there's a silent "you dummy" at the end?

No. Short bits of writing are often tone free so the emotional reaction one has to them usually has more to do with the reader's state of mind than the writer's intent. If you figured it out with that doc, you're obviously not a dummy. :) I'd have to keep looking for an example or a better explanation before I could write one but I wouldn't feel dumb, just annoyed.