If the video shows the Monza 2000 press conference, then Schumi wasn't crying for his mother since she passed away in 2003. Also, Monza's 2000 GP took place on 9/10/2000, on a Sunday. ( Most of us were at work when 9/11 happened. )
I am not sure the drivers did know the marshall was dead at that point, with Ralf saying "someone was hurt as we saw, but I don't know who it was".
In the 2000 season, Schumacher took 5 victories in the first 8 races, but in the next 5 races, McLaren won 4 times, and Barrichello once. Picture yourself a 2-time World Champion trying to assert yourself to victory with Ferrari over McLaren, 6 times. But 5 times in a row, you can't make it happen. The first 3 times, you don't even finish the race. The following 2 times, right when it matters for the championship, your main contender and 99 World Champion Mika Hakkinen takes 1st, and you 2nd. He's now ranking #1 for the drivers' title. And Ferrari hasn't had a championship title in 21 years, and they want it really, really bad. With all that pressure, you might get quite frustrated and ask yourself questions by then. I would.
And then, at the Italian GP, right in front of your own employer's public, and at a crucial time for the championship, you make it happen. It's got to be liberating.
Schumi went on to take the crown 2 GPs after that, at Suzuka.