So in Zenmanc's post they don't know who is the choice for LB, so No Idea is put there to make that point. That could easily be twisted by a poster to suggest, often humourously, that Zenmanc has actually selected a player called No Idea, as opposed to treating it as the placeholder it is.
mossideblue has gone one further and made a joke here suggesting that "No Idea" in Zenmanc's team is not only a player but actually Zenmanc themself, implying that Zenmanc has in mossideblue's opinion, no idea.