The lowest performing member of your team could be negative. Or they could be twice as good as the lowest performing person on some other team, or they could be above the industry average, meaning a 10x programmer becomes a 5x or 20x when the team changes.
I’ve always internalized as a “typical, competent programmer” rather than team-specific anything (Peopleware’s definition notwithstanding).
I believe this is incorrect. The baseline (or 1x) is the lowest-performing member of the team. At least that's how I learned the term.