I think this was stated in an earlier article.

This is pretty significant:

"At the time of his death, Rizzuto was believed by police to have drafted a “black list” of men in the Commisso family he wanted killed."

It makes sense that the Commisso approval was necessary for the Siderno group to back Montagna and others in their bid to overthrow the Rizzutos. It also makes sense that this Wolfpack Alliance need some backing from other Italian crime groups (perhaps the old Rizzuto group) to go after 'ndrangheta members.