I’m very familiar with those things and the posts that go up and down. What did they tell the gate guards? Given who is at that base, I could be wrong, but I’m thinking that you couldn’t just drive on without talking to someone.
The reports are short on details but the impression I get is there were no barriers or control arms at this gate, and that the intruders stopped at the gate, were refused entry and told to turn around, but instead proceeded into the installation.