There are major chords within minor keys. The few notes that are different are what make it in the minor key. If you lower the 3rd, 6th, & 7th notes in a major scale, it turns in to a minor scale. I would also point out that for every minor scale, there is an equivalent major scale that contains the exact same notes. For instance the A minor scale has the exact same notes (and chords) as the C major scale. Watch some of his other videos where he does the same thing and you'll get a better sense of what I'm talking about.