On my first reading of that it appears to rule that out on the statement "the above requirements shall be applied to each building".Not since I read Regulation 411.3.1.2.
Which is correct, extraneous parts much be bonded and in a manner to safely carry any fault currents.
But my argument is whether or not a service pipe from the main building, and bonded there, is an extraneous part. If the only potential it can introduce is that of the supply MET then it is no different from, say, an exterior light circuit, or some conduit between buildings carrying network cables, etc, which would normally be supplementary bonded if any doubts about touching two parts simultaneously.
Of course critical to that argument is knowledge of the pipe and its relationship to the supply point so the default to bond everything with 35mm or whatever is one approach, but if it does meet the criteria of originating (electrically speaking) from the main supply point then I don't see that as necessary as I see it could be classed as for conduit, cable tray, etc, going between buildings.