They were lifted one at a time -- but they were also intended to appear as a cloud of people rising across the great distance. Any one of us rooted in the muck of the comet could produce the same effect by physically throwing people who were not -- or at least, I believe they could. Zayne's thrown loose silverware on tabletops -- launching weightless individuals isn't a big step from there. (We also have not seen how well he has targeted them quite yet. If he were precision-guiding all of their independent movements after the throws, THAT would require more than one Jedi's brain...) As Force stunts go, we saw this one as having a lot of visual impact requiring not a lot of effort. If you were on a comet throwing playing cards into an unseen hat, it'd look equally strange to the observer waiting for the cards to get there.