Maybe not specifically to Assange, but they might be able to get close to that. An embassy probably wants to have separate, isolated networks to keep various classes of users apart. The top diplomats and officials who deal with the most important, most secret stuff on one. Another for lower level officials who deal with secret, but more routine stuff. A third that provides wifi for people visiting the embassy to use its services. Maybe a fourth for foreign diplomats attending meetings.

I could see them going beyond just building one physical network and then using firewalls to segment it into separate isolated logical networks and actually having separate physical connections for some of the networks, such as the one for visitors seeking services, and the one for foreign diplomats.

If they do have multiple physical networks, I'd expect they have Assange on one of the ones that is not important to the normal functioning of the embassy, such as one mostly used by people visiting to apply for visas and things like that. A large fraction of such visitors will have cellular internet on their phones and won't even notice that the embassy public wifi is broken.