This would be the man, since he was at the time major du génie.
Quickly reading the sources, At the Elster bridge, Monfort was ordered to mine the bridge. Being an engineering officer, he would be responsible for the actual placement, digging, placing of powder, fusing, etc of the explosives. Apparently, his orders did not clearly indicate when the mines were to be fired. Monfort left to get further orders on when to blow the bridge and the rest is history.
https://fr.wikipedia.org/wiki/Joseph_de_Puniet_de_Monfort , which has Monfort's memoirs listed as a source, states, Après avoir demandé à Berthier la veille de jeter d'autres ponts sur l'Elster (Berthier refusera, l'Empereur ne l'ayant pas ordonné), il reçoit l'ordre du général Dulauloy de détruire le pont du moulin reliant Lindenau à Leipzig dès que les troupes françaises l'auront franchi. which is bascially the same as seen in Thiers.
Since N. apparently having never commented on the incident, the scenario of B. not executing a direct order by N. seems to be the least likely. We also know that some writers, labeled as N. revisionists by Thiers, have been telling this story since before 1879 - which likely explains how it ended up in a German text.
Maybe B. at some point did mention this important subject to N., but, most reports are that N. was not very open to outside suggestions, so, without anything from N., and the only other known witness unfortunately was last seen.....