They are firing 10k people they have already hired, and not hiring for 5k roles where they haven't yet hired. So 10k are leaving, and the planned 5k they were going to add will not add. This means they are losing 10k.

No, it means that they won't hire these 5K in the first place.

I'm reading it as 10,000 people being fired and 5,000 job openings, some of which may have offers out, being cancelled.

No, it means they will not hire 5 k people they had planned to hire, and they'll let 10 k people go within their current workforce.