I thought chair letters were pretty standard. I’m not sure how someone applies to match a small field without having a sit down meeting with the chair at their home program. It’s a pretty standard thing and typically represents a summary of how the department views you. I was told by multiple interviewers that my chairman’s letter was what got me the interview, and from across the table it was only 3-4 lines of text. So they can be very powerful.
I would make an appointment ASAP and meet with the chair.