Yep. That is, almost to a word, the given definition.
And, sure, "some" grogs could take Self-Confident - tho', as with almost any Virtue, it should be the exception rather than the rule.
When I run a game, or co-SG in Troupe style, I present variety of different "caliber" grogs.
Ya gotcher peasants, real mud-grubbers and pig farmers, who may be good with a quarterstaff, or a knife in the kitchen (ahem) and that's practically a spear or a shortsword. Here ya go, good luck.
Then there are (highly?) trained individuals. Usually the above who have survived a campaign or two, or one way or another grew up in the profession, and are making a living at it. Quite capable.
But there's another tier above that (at least). For instance, a squad of Italian (Venetian, actually) crossbowmen - they charge more than an average grog, but are worth it. They have their own sergeant, they discipline themselves, know how to work as a group, they take pride in their status and abilities, they are the elite. And they are not stupid - no charging dragons for them, thanks. Not in their contract, read the fine print.
At some point, such a grog could begin to approach a Companion level of competence. If a grog has 3 Virtues, and a Companion 10, what lies between? Some folk, clearly.
When building shield grogs, I give them the Custos feat for free*, and also one more virtue that can be added with a balanced flaw. Makes them clearly above and beyond, which is why they're chosen.
(* Or if they get chosen from the masses. It's not like the mage picks them as Custos, and they run right out and lose an eye or a love in celebration.)
The point is that, yes, at some point between the pigfarmer with a spear and a Companion, a character can achieve enough to become more Self-Confident, even become quantifiably and qualifiably more than your average grog.