I think you are talking about Malcolm Greene Chace whose father was a stockholder in Berkshire Hathaway before Buffett bought into it. In fact, I believe that the senior Chace was a major stockholder in Berkshire Fine Spinning co before it merged with
Hathaway Mills to form Berkshire Hathaway. This is covered in Lowenstein's book on Warren Buffett.
He is just selling stock that his family has held for a longtime.