The instruction is part of crowd control. It is important that the people there believe whatever happened is a trivial interruption. If Hillary panics, the situation becomes more difficult to manage.
She looked scared. There is a view of the crowd that shows them with a sign. It looked like all they were doing was holding up a sign. SS didn’t circle Clinton like this
https://www.youtube.com/watch?v=eNOlR_kyrV4
Compare that to someone bum rushing the stage and trying to get to Trump.