Nuke silos and trolling?

I finally worked through one of the silos and got all the way to the launch sequence. Robots were working within maybe a minute of finishing. (Just trying to do it once and get the achievement) I go to look in the peepers/put the code and pick a spot and another player spawned in and killed me. Up until this point I had no idea other people could spawn into the silos and launch in place of somebody they killed?