And the mole he's referring to is probably Adler, based on the post-release story from Black Ops Cold War. And this wasn't the only Black Ops 6 teaser added to Warzone in the most recent update.

Toward the end of Call of Duty: Black Ops Cold War there will be a mission called Break On Through. Players can choose to obey Adler or let’s say get distracted with the mission. Don’t obey ...