I'm not following this very closely, but I've not seen any reports of diversions for domestic flights, so I think it'd be unlikely for international flights. The report is just for a ground stop, which is just a stop in departures; normally a ground stop would allow flights already in the air to travel to their normal destination.
That reasoning doesn't really make sense. A flight from outside the US that is inbound could divert to a non-US airport that isn't impacted by whatever is going on, depending on where they are and what their fuel status is. A domestic flight doesn't have a non-US airport to divert to.
(Sure, a flight near the Canadian or Mexican border could in theory divert to a Canadian or Mexican airport, but it's unlikely many people on those flights have their passports with them.)