SpaceX seems big enough that they pay for a self-hosted meeting suite. I've worked at a couple places that use WebEx that is self-hosted. You can only access it via dialing the number (from any phone) or by being on the VPN to see the shared presentation. Trying to log into the public version of WebEx gives you an unknown user error. Someone could still wardial their way into the call but it would require getting the non-public phone number and guessing the meeting number AND possibly guessing a meeting password.