Can't tell the actual pitch, he could have been at 45-degrees nose high, maybe even 60 but you can't tell from this camera angle.
They like to do that at airshows to stun/entertain the audience. It's doable from a good angle (if they are flying away)
Also, you can see that he could not sustain the climb rate, he leveled off once his airspeed dropped too low. "Zoom climb" anyone?
Cool stunt, though. I am not knocking it, merely pointing out that the camera angle embellishes it.
I have been in max perf takeoffs with 8000fpm zoom climbs in small jets before, it is a lot of fun!