Yup, not TPMS, my bad.
On the other hand, traction control icon would keep flashing on my old 5-series (no actual TPMS, direct or indirect) whenever all 4 tires were underinflated. I'm guessing it was somehow measuring that the rotational circumference was less than expected.
That's possible. If the diameter/circumference is less than it should be, it means the wheels have to spin faster, which it could interpret as slipping
