Corrected entry: When Apophis first enters SGC at the beginning, the worm hole shuts down. Then the fight between the SGC personnel and the Jaffa takes place. The scene then switches to some other part of the complex and back again. Suddenly there is an outgoing wormhole established. It is made clear throughout the show, that only very few aliens like the Asgard or the Nox can just establish a wormhole by waving the hand. Earth neither has a DHD (which is known to Apophis) nor does Apophis have access to the gate controls or was there enough time for the Jaffa to dial the gate by hand. Even assuming the scene switches giving enough time to enter the control room, the Jaffa can not be familiar with earth technology as to know how to initiate a dialing sequence on the computer.Christoph Galuschka
Corrected entry: Right at the start when the Goa'uld come through the stargate they leave back through the stargate after the firefight... with the dialing computers in another room not directly connected to the gate room. And of course they wouldn't know anything about computers. The only person who probably could have ordered the stargate to be opened is Hammond, but it is active even before Hammond meets the Goa'uld, so that leaves him out.