I would guess that the callout capsule probably only relates to hubscore in the way any text on the hub relates to hubscore. So text in there should be as relevant to the topic of the hub as text in a text capsule or in a link capsule.
It could be that it's good for your hubscore because using a variety of capsule types is good for your hubscore.
However, I would not recommend obsessing over hubscore at all.
The callout capsule is very good for highlighting quotes (with the source) and creating sections in your hub. Both are good for your visitors. And happy visitors helps your hubs and your hub account.