Burakucat or Wombat will be better at explaining it, than I.
As much as I would like to add to this latter discussion, I am very uncertain. I can see both "sides" and both make sense. The best I can "come up with" is an agreement with both!
Let us regard the low-pass filter, present in the "fibre cabinet", as the point where the E-side becomes the D-side.
Let us consider that either a battery contact or an earth contact fault exists 5 metres from the low-pass filter on the D-side. (Audible cross-talk, Ethel nattering to Enid, is noticed for the former fault whilst significant 50 Hz hum is heard for the latter.) The fault is hard and significant. (I suppose we could assume that a sub-standard jumpering task in the PCP was performed by an entity of one of those two sub-contracted companies.) Such a fault will effect the metallic pathway so as to be both telephony and broadband service degrading.
Let us consider that either a battery contact or an earth contact fault exists 5 metres from the low-pass filter on the E-side. The effect will be identical to the above for the telephony service. For the effect upon the broadband service, we have to consider the presence of the low-pass filter. My feeling is that the fault at 5 metres will probably have some effect on the broadband service but probably not so great. Now consider that the fault has its origin at the MDF (perhaps the snipped end of a jumper was accidentally dropped by a frames engineer and was not noticed bridging a pair of tags lower down the frame). I would expect the same effect on the telephony service but a significantly less effect on the broadband service. I postulate that the length of the E-side, coupled with the presence of the low-pass filter, will have offered some degree of "protection" to the broadband service.