Production queue means the specs of your car have been sent from one computer network (Tesla website and ordering) to the other (production). If Tesla's website was hacked or was under attack they wouldn't want this to affect the robots at the factory. Therefore these two networks are most likely disconnected which means they need to regularly move data from one to the other which also explains their unwillingness to make late changes.
This is a very interesting. It raises a lot of engineering questions, though. Are the systems which source the parts also independent of the factory computers? Does someone load up a USB stick every few weeks and walk it over to another network? One could share a computer network such that if someone "hacked" the website, they couldn't access the factory machines.
It could also be: they have a lot of factors which contribue to the ordering of the queue, e.g. P85, high priority customers, special orders, missing parts for a certain option, delivery logistics. But once a car gets into the queue, it would be very difficult to actually change the order. The fact that so many people went into the queue all at once could indicate that they were slowly getting up to speed after the re-tooling, and now they have in a place a longer term plan for the builds over the next two months. I'm not really satisfied with this explanation as either, but it's at least possible.