It wasn't just people noticing them from their desks (or joining them, for the sake of well-humoured fun). It was, as she says, "line of men sitting on one bench facing the hoopers and gawking at them".
I would find women doing hoola hoop in the office a bit odd. Maybe it really depends on the company culture, but I don't see how either things could be called inherently sexist or threatening.
I would find that a bit odd.