JoyCH might be right, but I have a different take on it.
In the 1-4-5-1 progressions, maybe he's treating every chord as a dominant 7th chord and using tritone substitution. For example, if C7-F7-G7-C7 (or 1-4-5-1) is the chord progression, maybe he's substituting that chord progression for F#7-B7-C#7-F#7. If we spell out the individual notes,
the 1 chord CEGA# becomes F#A#C#E
the 4 chord FACD# becomes BD#F#A
the 5 chord GBDF becomes C#FG#B
the 1 chord CEGA# becomes F#A#C#E
Try it out and you'll hear that the substitutions are totally legit. You can make those chords substitutions and still stay within the key of C with the melody. I think maybe he didn't say "tritone substitution" because that sounds too technical.