Wow, what an honourable way to go if you must. He traded unlikely survival with certain death and saved his girlfriend in the process. I feel bad for the mom, but still I don't know how many would be as brave as Netta to do that, even if you had adrenaline going.
While not diminishing the heroism, laying atop a grenade might be among the least bad ways to go during the attack. One instant you're there pumped on hero juice, the next instant you're gone. No leftover brain activity to experience who knows what while actively dying.
I've seen enough Ukranian drone drop videos with grenades landing on Russians to know that being on the receiving end is absolutely not immediately lights out.
Genuinely asking, how is that any better? And really, if you were trying to stop fragmentation from killing other people in a room wouldn't your actual core do a better job of that then your legs?
Different advice for different goals. If your goal is to survive, you want your vitals to be protected. If you want others to survive, might as well use your muscle and fat to absorb some of the kinetic energy.
The idea is obviously for everyone to lay flat with their legs facing the grenade, not just one person. If there's just you and one other person just force them to the ground. If you live in a dangerous place explain it to them beforehand and maybe even practice.