Comment by dragonwriter

I guess if you abused terminology to scale by risk then, something decaying faster but by a different mechandism could be “less radioactive”, e.g., for external exposure, an alpha emitter with a shorter half-life might be “less (dangerously) radioactive” than a beta emitter (of course, the reverse would be true for internal exposure.)

Can’t really think of any other way to rationalize that combination.