Rather than it just denoting keywords, I think this is just kind of showing that abilities and "classes" in this world are pretty much one and the same, which makes sense since the abilities inherited by the classmates are things like "absorption, divine light, insight" but also "hero, god of war, sword saint, etc". A character is just more likely to be called by a title that's a class-type one (Hero Miyamoto, Goddess of War Krusha/Nagisa, Witch Ordina) than something like "Absorption Nakatani".
I feel like we mostly know that they're not much different from skills though, since Nakatani absorbed Oni God from Onizuka, and Ray absorbing Goddess of War from Krusha is presumably how it was passed down to Nagisa (since the classmates' powers are fragments of Ray's power).
They're just pondering this chapter why Ray never bothered absorbing the Witch power, but considering typical witches I wouldn't be surprised if there was a downside to the skill he wanted to avoid (like Berserk's downside).