First line supervisor = chain of command AND support channel?

The Chain of Command topic states, under question 15, the following: "Who is the only member of both your chain of command the your NCO support channel? Your first line supervisor, section, squad or team leader"

Is this backed up by regulation somewhere? I've been unable to find this in any army publication, or really in any place other than sites quoting this study guide. If my chain of command is made up of commanders (people with command authority) how can my first line supervisor (an nco) be part of it?
Original Post
2-48. The second unique position is the squad, section or team leader. Possibly
the only NCO in the squad, section or team, he is the leader of his soldiers.
This NCO is the first link in both the NCO support channel and chain of
FM 7-22.7, Dec 2002. [Emphasis mine]
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