REAR BRAKE QUERY

ANYONE KNOW WHAT THIS IS.....SELLER SAYS ITS A BRAKE CONVERSION/MODIFICATION THAT WAS FITTED WHEN HE BOUGHT IT......ANY THOUGHTS?
https://scontent-lhr3-1.xx.fbcdn.net/v/ ... e=582DFCBD
https://scontent-lhr3-1.xx.fbcdn.net/v/ ... e=582DFCBD