That’s 5x the recommended max single dose, and 2.5x the recommended max daily dose (obviously depends from person to person and on body weight). I don’t think it would be lethal, but the symptoms would still suck - racing heart, shaking hands, quite often psychological symptoms like anxiety/panic… The worst part of caffeine OD is that it gets metabolized super slowly (half life 1.5-9.5 hours), so after 10 hours you might still experience those symptoms, and there’s simply nothing you can do. Speaking from experience here, although it was less than 1000mg. If this story is true (which it very well might be) I feel for OP.
Now I am concerned. When I say “correct me if I’m wrong”, I usually mean that literally.