Good catch. In case anyone doesn't quite see it, The pedia's categories list Leaders in it's plural form. This goes along nicely with the fact that, just like civ6, civ5 used the language of Civilizations and Leaders separately in it's product details quite often, despite the two always being connected. As we know, civ5 never had multiple leaders.
From the steam
G&K Feature list;
Why would the 9 new civilizations not include the leaders? One implies the other yet they advertize them anyway.
From
BnW Steam;
Once again, much like the language for the upcoming civ6 DLC, Civilizations and Leaders are both specified when they obviously one and the same.
There's a lot of language in civ5 that is very leader centric, and I think this is because over the evolution of the series, Civ has become as much about playing the leaders as it has the civilizations themselves. From the new footage we've seen, Civ6 (annoyingly) continues the trend of civ5 addressing the player during the loading screen as if
they themselves are the leader.
Though, I will admit that the Language for the Rough Rider UU is particularly strong. However, as someone else suggested, I'd see it much more likely to have a randomized leader option like in civ4 before multiple leaders return... like in ci4.
We'd probably be able to Play as Catherine de Medicci of the Aztec Empire before we see the return of Napoleon.