His conclusion is sound while yours is not. Korean is not a dialect of Chinese, which seems to be your implication. Neither is it a "branch" of a tree of which Chinese is the trunk. In linguistic terms it is called a "language isolate". In the past, linguists tended to group Korean and Japanese together; I believe largely for political reasons they have been separated--but that's another topic.

Korean uses many Chinese loan words (in the same way that English uses Greek loan words) but the sentence structure, pronunciation and grammar are totally different. You would not say English is a dialect or branch of Greek for the same reason.

I speak both Korean, Japanese and am currently studying Chinese. Korean does not sound like Mandarin at all because it is not a tonal language. It does sound similar to Mongolian and Manchurian. That is not surprising because the roots of Koreans (and probably their current language) come from the area north of Korea near Manchuria.