The info comes from the BTw database and I believe its original purpose was to stop ISPs being able to place a new order for a line which already had adsl. It served as a warning that a MAC key would be needed to migrate the service. It also flagged up if the line was LLU and also other things which may stop an order going through such as DACs.
At one point the LLU info was quite useful, but the only one Im allowed to specifically display now is TPON and Ive had to leave things as is rather than risk BT making me take it all down.