Well, it's not a glissando. That passage mimics in some way the effect of a glissando, but definitely, it's not. One way of percieve it, it's that not all notes are double notes, but there's an alternation between single and double notes, which makes it impossible to play using glissando technique.
Now, how is she able to play that passage? Marta Argerich is an outstanding pianist with an outstanding piano technique. And that's what that passage requires: a highly trained technique. I've never played Prokofiev's Third Piano Concerto so I can't do the fingering for that particular passage, but it reminds me to certain parts of Ravel's Jeux d'eau. At 0:50, you can see a passage where the right hand arpegiates playing double notes. That's usually played letting finger 1 play the lower two notes, and then 2-3 for the next two, 4-5 for the other two and then arpegiate. That's what I think the performer is intended to do while playing that passage in Porkofiev's Concerto, but with the added difficulty of playing double notes with both hands at an almost unhuman speed.
Not that I'm saying that double notes can't be played on a glissando. In fact, Ravel includes that technique a lot on most of his piano compositions, as it's shown in Ondine on his Gaspard de la Nuit, or in Alborada del Gracioso, where Richter looks like he plays those glissando almost effortlessly.