What does it mean to have a chanter pitched in C? Does that mean when all holes are closed it still plays a low D? or not.. Can you play with others? I know that a C scale has no sharps or flats, but other than that I don’t really understand it.
A chanter pitched in C is 2 steps below a concert pitch chanter in tuning. It has the C note as the bottom (bell note) all notes proceed up accordingly as in a D chanter. But, just to confuse you more, the bottom note is still referred to as “D”, and so on…
Thinking of it in more of a ‘music theory’ light:
D chanter- plays diatonic* scale in D starting on tonic D (D, E, F#, G, A, B, C#, D, and into the second octave)
C chanter- plays diatonic* scale in C starting on tonic C (C, D, E, F, G, A, B, C, and into the second octave)
This carries over to the other pitched chanters as well (B, Bb, Eb, G 
)
*naturally, a keyed chanter has the ability to play accidentals, making a chromatic scale
Easiest way to think of it is instead of playing a ‘D’ whistle, you’re playing a ‘C’ whistle.
It’s only complicated slightly by all pipers referring to the notes played as if they were played on a ‘D’ chanter, saves all that working out what the devil you’re actually playing when in B or Bb etc.