I agree with Jack. Dick makes perfect sense.

Richard, you seem to be mixing up discussion about a scale with discussion about a chord.

The point Dick is making is that the accompanist hears a tune centred on D with a major key feel so is expecting D major with a C# leading note.

However, he notices that all the C's are actually C natural so makes the false assumption the tune is actually D minor so starts playing Dmin chords rather than Dmaj. The result is discord as he will be playing Fnat on his guitar against F# in the tune and fiddles, flutes etc. will go bonkers and quite likely tell him where to get off if he doesn't desist.