Rossi's description only uses they/them pronouns, whereas other characters use he/him or she/her, indicating that this is in fact an intentional decision.

Given that Bell is a complete blank slate of a character, unlike past Call of Duty protagonists, you can desognate their gender before starting the campaign. To that end, you can either make them male, female, non-binary, or "classified". If you choose the latter two options, funnily enough, Bell will make no noise when injured. Non-binary people are built different, clearly.

https://www.thegamer.com/call-of-duty-black-ops-6-introduces-first-non-binary-operator-volta-rossi/

Ma foi...